Communication apparatus and communication method

ABSTRACT

Provided is a communication apparatus including a communication unit that receives frames including first information from a plurality of other communication apparatuses and transmits first frames including information indicating a first transmission time period to the plurality of other communication apparatuses, a control unit that determines the first transmission time period on the basis of the plurality of pieces of first information, and a processing unit that generates the first frames.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 16/245,693, filed on Jan. 11, 2019, which is acontinuation of U.S. patent application Ser. No. 15/520,067, filed onApr. 18, 2017, now U.S. Pat. No. 10,212,718, which is a National StageEntry of Patent Application No. PCT/JP2015/071919 filed on Aug. 3, 2015,which claims priority from prior Japanese Patent Application JP2014-219223 filed in the Japan Patent Office on Oct. 28, 2014, theentire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to communication apparatuses andcommunication methods.

BACKGROUND ART

Wireless local area networks (LANs), typified by IEEE (Institute ofElectrical and Electronics Engineers) 802.11, have in recent years beenwidespread, leading to an increase in the information amount oftransmitted contents and the number of wireless LAN-capable products.Therefore, to improve the efficiency of communication over an entirenetwork, the standard IEEE 802.11 is still being enhanced.

In the 802.11ac standard, which is an example enhanced version of thestandard IEEE 802.11, multi-user multi-input multi-output (MU-MIMO) isemployed for a downlink (DL). MU-MIMO is a technique for allowingtransmission of a plurality of signals during the same period of timethrough space-division multiplexing. The technique can improve theefficiency of use of frequencies, for example.

However, different communication apparatuses may transmit frames duringdifferent transmission time periods. In this case, the number ofmultiplexed frames fluctuates during a period of time when the framesare received. Therefore, the reception power of a communicationapparatus that receives multiplexed frames fluctuates during thereception time period. The fluctuation of the reception power may havean influence on the performance of reception. To address this problem, atechnique of transmitting frames during equal transmission time periodshas been proposed.

For example, Patent Literature 1 describes a communication apparatusthat appropriately adds a padding to a plurality of frames havingdifferent transmission time periods and thereby transmits the pluralityof frames during equal transmission time periods.

In addition, Patent Literature 2 describes a communication method inwhich a communication apparatus serving as an access point (AP)transmits uplink (UL) permission information designating a transmissiontime period of a UL frame and a communication apparatus receiving the ULpermission information transmits a UL frame over the designatedtransmission time period.

CITATION LIST Patent Literature

Patent Literature 1: JP 2010-263490A

Patent Literature 2: JP 2010-263493A

DISCLOSURE OF INVENTION Technical Problem

However, according to the inventions disclosed in Patent Literatures 1and 2, there are cases in which it is difficult to efficiently usewireless communication resources. For example, according to theinvention disclosed in Patent Literature 1, wireless communicationresources are consumed by a padding that is not relevant as data. Inaddition, according to the invention disclosed in Patent Literature 2,an AP does not know a transmission time period desired by each ofcommunication apparatuses that transmit UL frames at a point in time atwhich a transmission time period of the UL frames is designated, andthus may designate a transmission time period longer than the desiredtransmission time period. For this reason, there is a probability thatall of communication apparatuses which transmit UL frames will transmitpaddings.

Therefore, the present disclosure proposes a new and improvedcommunication apparatus and communication method that can reconcileefficient use of wireless communication resources with stabilization ofreception performance in wireless multiplex communication.

Solution to Problem

According to the present disclosure, there is provided a communicationapparatus including: a communication unit configured to receive framesincluding first information from a plurality of other communicationapparatuses and transmit first frames including information indicating afirst transmission time period to the plurality of other communicationapparatuses; a control unit configured to determine the firsttransmission time period on the basis of the plurality of pieces offirst information; and a processing unit configured to generate thefirst frames.

According to the present disclosure, there is provided a communicationmethod including: receiving frames including first information from aplurality of other communication apparatuses, and transmitting firstframes including information indicating a first transmission time periodto the plurality of other communication apparatuses; determining thefirst transmission time period on the basis of the plurality of piecesof first information; and generating the first frames.

Advantageous Effects of Invention

As described above, according to the present disclosure, a communicationapparatus and a communication method that can reconcile efficient use ofwireless communication resources with stabilization of receptionperformance in wireless multiplex communication are provided. Note thatthe effects described above are not necessarily limitative. With or inthe place of the above effects, there may be achieved any one of theeffects described in this specification or other effects that may begrasped from this specification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an example configuration of a communicationsystem according to an embodiment of the present disclosure.

FIG. 2 is a block diagram showing a schematic functional configurationof a communication station according to a first embodiment of thepresent disclosure.

FIG. 3 is a flowchart conceptually showing processing of thecommunication system according to the present embodiment.

FIG. 4 is a flowchart conceptually showing processing of a masterstation in an uplink transmission time period notification processaccording to the present embodiment.

FIG. 5 is a flowchart conceptually showing processing of a slave stationin the uplink transmission time period notification process according tothe present embodiment.

FIG. 6 is a flowchart conceptually showing processing of a masterstation performing an uplink multiplex transmission time perioddetermination process according to the present embodiment.

FIG. 7 is a flowchart conceptually showing processing of a masterstation in an uplink multiplex transmission and reception processaccording to the present embodiment.

FIG. 8 is a flowchart conceptually showing processing of a slave stationin the uplink multiplex transmission and reception process according tothe present embodiment.

FIG. 9 is a diagram showing an example of a frame exchange sequenceperformed by the communication system according to the presentembodiment.

FIG. 10 is a flowchart conceptually showing processing of a masterstation in an uplink transmission time period notification processaccording to a second embodiment of the present disclosure.

FIG. 11 is a flowchart conceptually showing processing of a masterstation performing an uplink multiplex transmission time perioddetermination process according to the present embodiment.

FIG. 12 is a flowchart conceptually showing processing of a slavestation in an uplink multiplex transmission and reception processaccording to the present embodiment.

FIG. 13 is a diagram showing an example of a frame exchange sequenceperformed by a communication system according to the present embodiment.

FIG. 14 is a diagram showing an example of a frame exchange sequenceperformed by a communication system according to a third embodiment ofthe present disclosure.

FIG. 15 is a block diagram showing an example schematic configuration ofa smartphone.

FIG. 16 is a block diagram showing an example schematic configuration ofa car navigation device.

FIG. 17 is a block diagram showing an example schematic configuration ofa wireless access point.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, (a) preferred embodiment(s) of the present disclosure willbe described in detail with reference to the appended drawings. In thisspecification and the appended drawings, structural elements that havesubstantially the same function and structure are denoted with the samereference numerals, and repeated explanation of these structuralelements is omitted.

Also, in the present specification and the drawings, different numbersare attached to the end of the same reference number to distinguish aplurality of components having substantially the same functionalconfiguration from each other in some cases. For example, a plurality ofcomponents having substantially the same function are distinguished,such as communication stations 10#1 and 10#2, as necessary. However,when it is unnecessary to distinguish substantially the same functionalconfigurations, only the same reference number is given thereto. Forexample, when it is not particularly necessary to distinguish thecommunication stations 10#1 and 10#2 from each other, they are simplyreferred to as communication stations 10.

In addition, the description will be made in the following order.

1. Overview of communication system according to embodiment of presentdisclosure

2. First embodiment (example of space-division multiplex communication)

3. Second embodiment (example of dividing UL frame)

4. Third embodiment (example of multicast communication)

5. Fourth embodiment (example of frequency-division multiplexcommunication)

6. Application example

7. Conclusion

1. OVERVIEW OF COMMUNICATION SYSTEM ACCORDING TO EMBODIMENT OF PRESENTDISCLOSURE

Firstly, an overview of a communication system according to anembodiment of the present disclosure will be described with reference toFIG. 1. FIG. 1 is a diagram showing an example configuration of thecommunication system of the embodiment of the present disclosure.

The communication system is configured with a plurality of communicationapparatuses (hereinafter, also referred to as communication stations)10. The communication stations 10 have a wireless communication functionand perform communication using multiplexing. Also, the communicationstations 10 operate as APs or terminals. Hereinafter, a communicationstation operating as an AP will also be referred to as a master station,and communication stations operating as terminals will be referred to asslave stations. For this reason, in the communication system,one-to-multiple communication using multiplexing is possible between themaster station and the slave stations. Here, communication from themaster station to the slave stations is referred to as downlink (DL),and communication from the slave stations to the master station isreferred to as uplink (UL).

For example, as shown in FIG. 1, the communication system may include aplurality of communication stations 10#0 to 10#4. The communicationstation 10#0 which is a master station and the communication stations10#1 to 10#4 which are slave stations are connected through wirelesscommunication and directly transmit and receive frames to and from eachother. For example, the master station 10#0 is a communication stationconforming to IEEE802.11ac, and performs space-division multiple access(SDMA) using an adaptive array antenna.

Here, when transmission time periods of frames separately transmitted bya plurality of slave stations are different, the number of multiplexedframes generally fluctuates during a period of time in which the framesare received. For this reason, reception power of a master station thatreceives the frames drastically changes during the reception timeperiod, and the change in the reception power may have an effect onreception performance of the master station.

To address this problem, a method in which a master station designates atransmission time period of a UL frame and slave stations maketransmission time periods of UL frames the same as the designatedtransmission time period has been proposed. However, according to thismethod, the master station does not know a transmission time perioddesired by each of the slave stations that transmit UL frames at a pointin time at which a transmission time period of the UL frames isdesignated, and thus may designate a transmission time period longerthan the desired transmission time period. For this reason, there is aprobability that all of the slave stations which transmit UL frames willtransmit paddings. On the other hand, when a transmission time periodshorter than the desired transmission time period is designated, a ULframe to be transmitted does not fit in the designated transmission timeperiod, and there is also a probability that it will be difficult for aslave station to transmit the UL frame.

Therefore, the present disclosure proposes a communication apparatus anda communication method that can reconcile efficient use of wirelesscommunication resources with stabilization of reception performance inwireless multiplex communication. Details thereof will be describedbelow. Here, although an example of a communication system in which thecommunication station 10#0 is a master station is described in FIG. 1,another communication station 10 may be a master station, or thecommunication station 10#0 may be a communication station having aplurality of direct links with other communication stations 10#1 to10#4. In the latter case, the aforementioned UL may be replaced with“simultaneous transmission from one station to a plurality of stations,”and the aforementioned UL may be replaced with “simultaneoustransmission from a plurality of stations to one station.” Also, forconvenience of description, communication stations 10 according to firstto fourth embodiments are distinguished by attaching numberscorresponding to the embodiments to the ends thereof, such as acommunication station 10-1 and a communication station 10-2.

2. FIRST EMBODIMENT (EXAMPLE OF SPACE-DIVISION MULTIPLEX COMMUNICATION)

A communication system according to an embodiment of the presentdisclosure has been described above. Next, communication stations 10-1according to a first embodiment of the present disclosure are described.In the present embodiment, a master station among the communicationstations 10-1 determines a permitted transmission time period of a ULframe on the basis of information indicating transmission time periodsreceived from slave stations. Thereafter, the slave stations transmit ULframes on the basis of the permitted transmission time period.

2-1. Configuration of Communication Apparatus

First, a configuration of a communication station 10-1 according to thefirst embodiment of the present disclosure will be described withreference to FIG. 2. FIG. 2 is a block diagram showing a schematicfunctional configuration of a communication station 10-1 according tothe first embodiment of the present disclosure.

As shown in FIG. 2, the communication station 10-1 includes a dataprocessing unit 11, a communication unit 12, and a control unit 17.First, basic functions of the communication station 10-1 will bedescribed.

((Basic Functions))

The data processing unit 11 performs a process for transmission andreception of data. Specifically, the data processing unit 11 generates aframe on the basis of data from a higher-level layer of communication,and provides the generated frame to a modulation/demodulation unit 13described below. For example, the data processing unit 11 generates aframe (or packets) from data, and performs processes, such as additionof a MAC header for media access control (MAC), addition of an errordetection code, and the like, on the generated frame. The dataprocessing unit 11 also extracts data from a received frame, andprovides the extracted data to a higher-level layer of communication.For example, the data processing unit 11 obtains data by performing, ona received frame, analysis of a MAC header, detection and correction ofcode error, a reordering process, and the like

As shown in FIG. 2, the communication unit 12 includes amodulation/demodulation unit 13, a signal processing unit 14, a channelestimation unit 15, and radio interface units 16.

The modulation/demodulation unit 13 performs a modulation process andthe like on a frame. Specifically, the modulation/demodulation unit 13performs encoding, interleaving, and modulation on a frame provided bythe data processing unit 11, in accordance with coding and modulationschemes and the like set by the control unit 17, to generate a symbolstream. Thereafter, the modulation/demodulation unit 13 provides thegenerated symbol stream to the signal processing unit 14. Themodulation/demodulation unit 13 also performs demodulation and decodingor the like on the symbol stream provided by the signal processing unit14 to obtain a frame, and provides the obtained frame to the dataprocessing unit 11 or the control unit 17.

The signal processing unit 14 performs a process involved inspace-division multiplex communication. Specifically, the signalprocessing unit 14 performs a signal process involved in spaceseparation, on a symbol stream provided by the modulation/demodulationunit 13, and provides symbol streams obtained by the process to therespective radio interface units 16. The signal processing unit 14 alsoperforms a spatial process, such as a symbol stream separation processor the like, on symbol streams obtained from the radio interface units16, and provides a symbol stream obtained by the process to themodulation/demodulation unit 13.

The channel estimation unit 15 estimates a channel gain. Specifically,the channel estimation unit 15 calculates complex channel gaininformation from a preamble part or training signal part of a signalcontained in the symbol stream obtained from the radio interface unit16. Note that the calculated complex channel gain information isprovided to the modulation/demodulation unit 13 and the signalprocessing unit 14 through the control unit 17, and is used in amodulation process and a space separation process or the like.

The radio interface unit 16, which includes an antenna, transmits andreceives a signal through the antenna. Specifically, the radio interfaceunit 16 converts a signal contained in a symbol stream provided from thesignal processing unit 14, into an analog signal, and performsamplification, filtering, and frequency upconversion on the analogsignal. Thereafter, the radio interface unit 16 transmits the processedsignal through the antenna. The radio interface unit 16 also performs,on a signal from the antenna, reverse processes to those which areperformed for signal transmission, such as frequency downconversion,digital signal conversion, and the like, and provides the signalobtained by the processes to the channel estimation unit 15 and thesignal processing unit 14.

Here, a slave station may not include the signal processing unit 14, thechannel estimation unit 15, and the two radio interface units 16. Also,the modulation/demodulation unit 13, the signal processing unit 14, thechannel estimation unit 15, and the radio interface units 16 arecollectively referred to as the communication unit 12.

The control unit 17 controls an overall operation of the communicationstation 10-1. Specifically, the control unit 17 transfers informationbetween each function, sets communication parameters, and schedulesframes (or packets) in the data processing unit 11, for example.

((Functions of Case of Operating as Master Station))

Next, functions of a case in which the communication station 10-1operates as a master station will be described in detail.

(Functions Relating to Uplink Transmission Time Period NotificationProcess)

The data processing unit 11 generates a frame relating to priorcommunication for communication using space-division multiplexing.Specifically, the data processing unit 11 generates a frame whichrequests a slave station to transmit a frame including a referencesignal for estimating an antenna weight used for space-divisionmultiplexing. For example, the data processing unit 11 generates atraining request (TRQ) frame.

Further, the data processing unit 11 includes information indicating aplurality of slave stations which are destinations of the TRQ frame. Forexample, the data processing unit 11 may include information indicatingeither of MAC addresses of the slave stations and a group identifier forgrouping the slave stations in the TRQ frame. Here, the group identifieris considered to be known to the slave stations.

Also, the data processing unit 11 includes information for separatingrespective frames, for example, training feedback (TFB) frames,transmitted from the slave stations as responses to the TRQ frame. Forexample, the data processing unit 11 includes information designating anencoding method for orthogonalizing reference signals included in theTFB frames in the TRQ frame. Here, a method of separating TFB frames isnot limited to the aforementioned method, and a variety of generalmethods may be used.

Also, the data processing unit 11 acquires antenna weights from TFBframes received by the communication unit 12. Specifically, when TFBframes are received by the communication unit 12, the communication unit12 separates the TFB frames on the basis of the information designatingthe encoding method and encoded reference signals included in the TFBframes. Thereafter, the data processing unit 11 acquires antenna weightsof the respective slave stations on the basis of the respectivereference signals of the separated TFB frames. Here, the acquiredantenna weights are managed by the control unit 17.

The communication unit 12 performs transmission and reception of framesrelating to prior communication for space-division multiplexingcommunication. Specifically, the communication unit 12 transmits the TRQframe generated by the data processing unit 11 to each of the slavestations, and receives TFB frames from the respective slave stations asresponses to the TRQ frame.

(Functions Relating to Uplink Multiplex Transmission Time PeriodDetermination Process)

The control unit 17 determines a permitted transmission time period onthe basis of information (hereinafter, also referred to as reversedirection request (RDR) information) indicating transmission timeperiods (hereinafter, also referred to as requested transmission timeperiods) which is first information obtained from a plurality of slavestations. Here, the RDR information indicates a time length desired tobe used in transmission of user data retained by each slave station.Also, the user data may be a data frame or a management frame.Specifically, the control unit 17 determines the permitted transmissiontime period on the basis of a transmission time period (hereinafter,also referred to as R_(max)) longer than other transmission time periodsamong transmission time periods indicated by respective pieces of RDRinformation included in TFB frames received by the communication unit 12from the plurality of slave stations.

For example, the control unit 17 determines a permitted transmissiontime period on the basis of an expression R_(max)+T_(ack). Here, T_(ack)indicates a transmission time period (hereinafter, also referred to asan ACK transmission time period) of an acknowledgement (hereinafter,also referred to as ACK) frame of a trigger frame from a master stationto a slave station. Here, modulation schemes or modulation rates of anacknowledgement frame in respective slave stations are considered to bethe same.

An example in which the control unit 17 determines a permittedtransmission time period on the basis of R_(max) has been describedabove, but the control unit 17 may determine a permitted transmissiontime period on the basis of a mode of transmission time periodsindicated by respective pieces of RDR information included in TFB framesreceived from a plurality of slave stations. In this case, efficiency inuse of wireless communication resources can be improved in comparisonwith a case in which UL frames are transmitted from slave stations usingthe permitted transmission time period based on R_(max), in other words,a maximum, depending on bias of transmission time periods indicated bythe RDR information.

Also, when the determined permitted transmission time period is greaterthan a threshold value, the control unit 17 may determine a permittedtransmission time period to be a transmission time period which is equalto or less than the threshold value. For example, when the determinedpermitted transmission time period R_(max)+T_(ack) exceeds a thresholdvalue G_(limit), the control unit 17 determines the threshold valueG_(limit) as a permitted transmission time period. In other words, thecontrol unit 17 determines a permitted transmission time period on thebasis of, for example, min(G_(limit), R_(max)+T_(ack)). In this case,the permitted transmission time period is reduced to the threshold valueor less, and thus it is possible to cope with even a case in which atransmission time period that can be allocated to slave stations issuppressed due to the status of wireless communication resources, acommunication policy of the master station, or the like.

Further, the threshold value G_(limit) may be determined on the basis ofinformation indicating a spare time of a wireless channel or the amountof traffic relating to communication of the master station. For example,the status of wireless communication resources may be indicated by atime ratio (hereinafter, also referred to as an idle time ratio) ofcarrier sense results in the master station that are determined to beidle or busy, the amount of communication with a communication stationconnected to the master station, or the like. Thereafter, the thresholdvalue G_(limit) is determined on the basis of the idle time ratio, theamount of traffic, or the like, so that excessive resources are notallocated for transmission of UL frames from slave stations and othercommunication is not hindered.

Also, an example in which RDR information is information indicating atransmission time period has been described above, but RDR informationmay be information which enables calculation of a transmission timeperiod. For example, RDR information may be a set of informationindicating the amount of data to be transmitted and informationindicating a modulation rate. Also, an example in which RDR informationis information indicating a transmission time period itself has beendescribed above, but RDR information may be information obtained byquantizing a transmission time period to a predetermined level ofgranularity.

(Functions Relating to Uplink Multiplex Transmission and ReceptionProcess)

As a processing unit, the data processing unit 11 generates a frameincluding information (hereinafter, also referred to as reversedirection grant (RDG) information) indicating a permitted transmissiontime period, which is a first transmission time period, as a firstframe. Specifically, the data processing unit 11 generates a DL frameincluding RDG information indicating the permitted transmission timeperiod determined by the control unit 17 for each slave station. Here,the corresponding DL frame is a trigger for transmission of a UL frameof a slave station, and thus will hereinafter also be referred to astrigger frame.

For example, the data processing unit 11 may include RDG information ina duration/ID field or the like of a MAC header of a trigger frame.Here, a method of adding RDG information is not limited thereto. Forexample, the data processing unit 11 may add a separate field to atrigger frame and include RDG information in the added field. Also, thecorresponding trigger frame may be described below as a data frame.However, the corresponding trigger frame is not limited thereto and maybe other frames, such as a control frame, a management frame, or thelike.

The communication unit 12 transmits corresponding frames to a pluralityof slave stations by multiplexing the frames including informationindicating the permitted transmission time period. Specifically, usingan antenna weight of each slave station known through a TFB frame, thecommunication unit 12 space-division multiplexes respective framesgenerated by the data processing unit 11 and including informationindicating the permitted transmission time period.

((Functions of Case of Operating as Slave Station))

Next, functions of a case in which the communication station 10-1operates as a slave station will be described in detail.

(Functions Relating to Uplink Transmission Time Period NotificationProcess)

The data processing unit 11 generates a frame as a response to a framereceived from a master station and relating to prior communication forspace-division multiplexing communication. Specifically, the dataprocessing unit 11 acquires information indicating slave stations whichare destinations of a frame included in the corresponding frame receivedfrom the master station, and determines whether correspondinginformation includes the slave station. When the correspondinginformation includes the slave station as a destination, the dataprocessing unit 11 generates a frame including a reference signal as aresponse to the corresponding frame. For example, the data processingunit 11 generates a TFB frame as a response to a TRQ frame received fromthe master station. Here, the reference signal may be inserted into apreamble part.

Further, the data processing unit 11 adds processing to the referencesignal on the basis of information for separating TFB frames. Forexample, the data processing unit 11 encodes the reference signalincluded in the TFB frame in accordance with an encoding method includedin the TRQ frame.

Also, the data processing unit 11 includes RDR information in the TFBframe. For example, the data processing unit 11 generates the RDRinformation on the basis of a transmission time period determined by thecontrol unit 17, and includes the generated RDR information in the TFBframe. Here, the RDR information indicates a time length desired to beused in transmission of user data retained by each slave station. Also,the user data may be a data frame or a management frame.

Like in the case of a master station, the communication unit 12 performstransmission and reception of frames relating to prior communication forspace-division multiplexing communication. Specifically, thecommunication unit 12 receives a TRQ frame from the master station, andtransmits the TFB frame generated by the data processing unit 11 to themaster station a predetermined time after reception of the TRQ frame.The corresponding predetermined time is the same for each slave stationand may be, for example, a short inter-frame space (SIFS) or the like.Here, the master station may provide a notification of the correspondingpredetermined time through a TRQ frame or the like, or the correspondingpredetermined time may be a time previously stored in slave stations.

The control unit 17 determines a requested transmission time period thatthe master station is notified of. Specifically, the control unit 17determines the requested transmission time period on the basis of theamount of data to be transmitted. For example, the control unit 17calculates the amount of data to be transmitted with reference to atransmission buffer. Thereafter, the control unit 17 determines therequested transmission time period on the basis of the calculated amountof data and a modulation scheme.

(Functions Relating to Uplink Multiplex Transmission and ReceptionProcess)

The data processing unit 11 generates a frame on the basis of thepermitted transmission time period. Specifically, the data processingunit 11 generates the frame so that a transmission time period becomesthe permitted transmission time period. More specifically, the dataprocessing unit 11 generates the UL frame to which an acknowledgementframe of a trigger frame received from the master station is connectedso that a transmission time period of the UL frame becomes the permittedtransmission time period.

For example, the data processing unit 11 first generates a data frame onthe basis of data to be transmitted, and subsequently generates an ACKframe of the trigger frame. Thereafter, the data processing unit 11generates a UL frame by connecting the data frame and the ACK frametogether. Here, a position of the ACK frame in the UL frame isarbitrary.

Further, when a transmission time period of the UL frame is shorter thanthe permitted transmission time period, the data processing unit 11makes the transmission time period of the UL frame the same as thepermitted transmission time period by adding a padding to the UL frame.

Although an example in which a transmission time period of a generatedUL frame is equal to or shorter than a permitted transmission timeperiod has been described above, the data processing unit 11 may adjustthe UL frame when the transmission time period of the generated UL frameexceeds the permitted transmission time period. Specifically, the dataprocessing unit 11 separates a data frame from the UL frame.

For example, the data processing unit 11 calculates a transmission timeperiod (hereinafter, also referred to as an available transmission timeperiod) which is obtained by subtracting an ACK transmission time periodfrom the transmission time period of the UL frame, and determineswhether a transmission time period of the data frame exceeds theavailable transmission time period. When it is determined that thetransmission time period of the data frame exceeds the availabletransmission time period, the data processing unit 11 divides the dataframe using a method such as fragmentation so that transmission timeperiods become equal to or shorter than the available transmission timeperiod. Here, when the data frame is an aggregation frame, the dataprocessing unit 11 may change the data frame by disconnecting some ofsubframes of the data frame so that transmission time periods of thedata frame become equal to or shorter than the available transmissiontime period.

In this case, even when a new transmission request is generated afternotification of a requested transmission time period or the permittedtransmission time period is suppressed to a threshold value or less inthe master station, an opportunity for transmission is ensured, and itis possible to improve communication efficiency.

2-2. Processing of Communication Apparatus

Next, processing of the communication system and the communicationstations 10-1 according to the present embodiment will be described withreference to FIGS. 3 to 8. First, the flow of processing of thecommunication system will be described with reference to FIG. 3. FIG. 3is a flowchart conceptually showing processing of the communicationsystem according to the present embodiment.

(Flow of Overall Process)

First, an uplink transmission time period notification process isperformed in the communication system (step S101). Specifically, a TRQframe is transmitted from a master station to the slave stations, andTFB frames including RDR information indicating requested transmissiontime periods are transmitted from the slave stations to the masterstation as responses to the corresponding TRQ frame. For example,processes are performed as shown in FIGS. 4 and 5.

Next, an uplink multiplex transmission time period determination processis performed in the communication system (step S102). Specifically, apermitted transmission time period is determined at the master stationon the basis of the RDR information included in the TFB frames receivedfrom the slave stations. For example, a process is performed as shown inFIG. 6.

Next, an uplink multiplex transmission and reception process isperformed in the communication system (step S103). Specifically, triggerframes including the RDR information indicating the permittedtransmission time period are transmitted from the master station to theslave stations, and a UL frame based on the permitted transmission timeperiod is transmitted from each of the slave stations to the masterstation. For example, processes are performed as shown in FIGS. 7 and 8.

(Flow of Uplink Transmission Time Period Notification Process)

Details of an uplink transmission time period notification process whichis a process of step S101 in FIG. 3 will be described next. First,processing of a master station in the uplink transmission time periodnotification process will be described with reference to FIG. 4. FIG. 4is a flowchart conceptually showing processing of a master station in anuplink transmission time period notification process according to thepresent embodiment.

First, the master station generates a TRQ frame (step S201).Specifically, the data processing unit 11 generates the TRQ frameincluding information indicating the slave stations which aredestinations of the TRQ frame, and information indicating a method ofencoding a reference signal.

Next, the master station transmits the TRQ frame (step S202).Specifically, the communication unit 12 transmits the TRQ framegenerated by the data processing unit 11 to each of the slave stations.

Next, the master station determines whether a TFB frame has beenreceived within a predetermined time (step S203). Specifically, thecontrol unit 17 waits the predetermined time to receive TFB frames.Thereafter, when the corresponding predetermined time elapses, thecontrol unit 17 determines whether a TFB frame is received from each ofthe slave stations which are destinations of the TRQ frame. For example,when TFB frames are received during the corresponding predeterminedtime, the communication unit 12 separates the TFB frames in accordancewith the encoding method known to the slave stations through the TRQframe. Thereafter, when the corresponding predetermined time elapses,the control unit 17 determines whether the TFB frames obtained byseparation have been received from all of the slave stations which arethe destinations of the TRQ frame.

When it is determined that TFB frames have not been received within thepredetermined time, the master station determines whether the number ofretransmissions of the TRQ frame is equal to or smaller than apredetermined number of times (step S204). Specifically, when it isdetermined that no TFB frame has been received from any one of the slavestations which are the destinations of the TRQ frame within thepredetermined time, the control unit 17 determines whether the number ofretransmissions of the TRQ frame is equal to or smaller than thepredetermined number of times.

When it is determined that the number of retransmissions of the TRQframe is equal to or smaller than the predetermined number of times, themaster station returns to step S202 and performs retransmission of theTRQ frame. Specifically, when it is determined that the number ofretransmissions of the TRQ frame is equal to or smaller than thepredetermined number of times, the control unit 17 causes thecommunication unit 12 to retransmit the TRQ frame to a slave stationrelating to a TFB frame which has not been received. Here, the TRQ framemay be retransmitted to all of the slave stations which are the originaldestinations of the TRQ frame.

When it is determined in step S203 that TFB frames have been receivedwithin the predetermined time, the master station continues the processand changes over to an uplink multiplex transmission time perioddetermination process which is a next process. Here, when it isdetermined in step S204 that the number of retransmissions of the TRQframe exceeds the predetermined number of times, the master station endsthe process without retransmitting the TRQ frame.

Processing of a slave station in an uplink transmission time periodnotification process will be described next with reference to FIG. 5.FIG. 5 is a flowchart conceptually showing processing of a slave stationin the uplink transmission time period notification process according tothe present embodiment.

First, a slave station determines whether a TRQ frame addressed to theslave station has been received (step S301). Specifically, when a TRQframe is received by the communication unit 12, the data processing unit11 determines whether the corresponding TRQ frame is a TRQ frameaddressed to the slave station with reference to information indicatinga slave station which is a destination included in the TRQ frame.

When it is determined that a TRQ frame addressed to the slave stationhas been received, the slave station calculates the amount of data to betransmitted to a TRQ transmission source (step S302). Specifically, whena TRQ frame addressed to the slave station is received, the control unit17 calculates the amount of data to be transmitted with reference to atransmission buffer.

Next, the slave station determines a requested transmission time periodon the basis of the amount of data and a modulation scheme (step S303).Specifically, the control unit 17 determines a requested transmissiontime period on the basis of the calculated amount of data and a selectedmodulation scheme. For example, the control unit 17 determines therequested transmission time period on the basis of a modulation ratedecided by the amount of data and the modulation scheme.

Next, the slave station generates a TFB frame including informationindicating the requested transmission time period (step S304).Specifically, the data processing unit 11 generates RDR informationindicating the requested transmission time period determined by thecontrol unit 17. Thereafter, the data processing unit 11 generates theTFB frame including a reference signal encoded in accordance with anencoding scheme known through the TRQ frame and the RDR information.

Next, the slave station transmits the TFB frame a predetermined timeafter reception of the TRQ frame (step S305). Specifically, the controlunit 17 causes the communication unit 12 to transmit the TFB frame tothe master station when the predetermined time elapses after the TRQframe is received.

(Flow of Uplink Multiplex Transmission Time Period DeterminationProcess)

Details of an uplink multiplex transmission time period determinationprocess which is the process of step S102 in FIG. 3 will be describedwith reference to FIG. 6 continuously. FIG. 6 is a flowchartconceptually showing processing of a master station performing an uplinkmultiplex transmission time period determination process according tothe present embodiment.

First, the master station acquires an antenna weight and a requestedtransmission time period from each TFB frame (step S401). Specifically,the data processing unit 11 calculates antenna weights on the basis ofreference signals of the TFB frames separated by the communication unit12. Also, the data processing unit 11 acquires information indicatingrequested transmission time periods from the TFB frames.

Next, the master station specifies a maximum value among the acquiredrequested transmission time periods (step S402). Specifically, thecontrol unit 17 compares the requested transmission time periodsacquired from the TFB frames with each other and specifies a maximumvalue R_(max) among the corresponding requested transmission timeperiods.

Next, the master station determines whether there is a threshold valueof a permitted transmission time period (step S403). Specifically, thecontrol unit 17 determines whether or not a threshold value of apermitted transmission time period has been set. Here, whether or not athreshold value of a permitted transmission time period has been set andthe value may be previously stored in a storage unit or the likeseparately provided in the communication station 10-1, or may be changedin accordance with the status of wireless communication resources, acommunication policy of the master station, or the like. Here, thestatus of wireless communication resources may be indicated by, forexample, an idle time ratio per unit time of carrier sensing at themaster station, the amount of traffic between the master station and apartner connected to the master station, or the like. Thereafter, thethreshold value G_(limit) is set on the basis of the idle time ratio,the amount of traffic, or the like so that excessive resources are notallocated for transmission of UL frames from slave stations and othercommunication is not hindered. Also, when it is fixed whether or not athreshold value has been set, the present process may not be performed.

When it is determined that there is no threshold value of a permittedtransmission time period, the master station determines a permittedtransmission time period on the basis of the maximum value of requestedtransmission time periods and an ACK transmission time period (stepS404). Specifically, the control unit 17 determines the sum of themaximum value R_(max) of requested transmission time periods and the ACKtransmission time period T_(ack) as a permitted transmission timeperiod.

When it is determined that there is a threshold value of a permittedtransmission time period, the master station determines a permittedtransmission time period on the basis of the maximum value of requestedtransmission time periods, the ACK transmission time period, and thethreshold value (step S405). Specifically, the control unit 17determines the smaller value between the sum of the maximum valueR_(max) of requested transmission time periods and the ACK transmissiontime period T_(ack) and the threshold value G_(limit) of a permittedtransmission time period as a permitted transmission time period.

(Flow of Uplink Multiplex Transmission and Reception Process)

Details of an uplink multiplex transmission and reception process whichis the process of step S103 in FIG. 3 will be described next. First,processing of the master station in the uplink multiplex transmissionand reception process will be described with reference to FIG. 7. FIG. 7is a flowchart conceptually showing processing of a master station in anuplink multiplex transmission and reception process according to thepresent embodiment.

First, the master station generates trigger frames including informationindicating the permitted transmission time period (step S501).Specifically, the data processing unit 11 generates RDG informationindicating the permitted transmission time period determined by thecontrol unit 17 and generates trigger frames including the generated RDGinformation.

Next, the master station transmits the trigger frames which arespace-division multiplexed using the antenna weights (step S502).Specifically, the communication unit 12 performs a process forspace-division multiplexing the trigger frames using the calculatedantenna weights and transmits the processed trigger frames to the slavestations.

Next, the master station determines whether UL frames have been receivedwithin a predetermined time (step S503). Specifically, the control unit17 waits the predetermined time to receive UL frames. At this time, thecontrol unit 17 retains the antenna weights which have been used totransmit the trigger frames. Thereafter, when the correspondingpredetermined time elapses, the control unit 17 determines whether a ULframe has been received from each of the slave stations which aredestinations of the trigger frames. For example, when UL frames arereceived during the corresponding predetermined time, the communicationunit 12 separates the UL frames using the retained antenna weights.Thereafter, the control unit 17 determines whether UL frames obtained byseparation have been received from all of the slave stations which arethe destinations of the trigger frames after lapse of the correspondingpredetermined time. In the present process, the data processing unit 11may acquire data from the UL frames.

When it is determined that UL frames have been received within thepredetermined time, the master station transmits ACK frames of thereceived UL frames (step S505). Specifically, when it is determined thatUL frames have been received within the predetermined time, the dataprocessing unit 11 generates ACK frames corresponding to each of the ULframes. Thereafter, the communication unit 12 performs a process forspace-division multiplexing the generated ACK frames and transmits theprocessed ACK frames to the slave stations.

When it is determined that UL frames have not been received within thepredetermined time, the master station determines whether the number ofretransmissions of the trigger frames is equal to or smaller than apredetermined number of times (step S505). When it is determined thatthe corresponding number of retransmissions of the trigger frames isequal to or smaller than the predetermined number of times, the masterstation returns to step S502 and retransmits the trigger frames. Here,since the process has substantially the same details as the process ofstep S204 in FIG. 4, the description thereof will be omitted.

Processing of the slave station in the uplink multiplex transmission andreception process will be described next with reference to FIG. 8. FIG.8 is a flowchart conceptually showing processing of a slave station inthe uplink multiplex transmission and reception process according to thepresent embodiment.

First, the slave station waits until a trigger frame is received (stepS601). When a trigger frame is received, the slave station acquires thepermitted transmission time period from the received trigger frame (stepS602). Specifically, when a trigger frame is received, the communicationunit 12 corrects a frequency offset of a reference oscillator withrespect to the master station using a signal in a preamble (a physicallayer (PHY) preamble or the like) of the corresponding trigger frame.This is because it may be very difficult to extract a signal from areceived transmission wave when frequencies of the master station andthe slave station are not identical to each other. Thereafter, the dataprocessing unit 11 acquires RDG information indicating a permittedtransmission time period from the corresponding trigger frame.

Next, the slave station calculates an available transmission time periodof a data frame on the basis of the permitted transmission time period(step S603). Specifically, the control unit 17 calculates an availabletransmission time period of a data frame by calculating a differencebetween the permitted transmission time period and the ACK transmissiontime period.

Next, the slave station determines whether a transmission time period ofa data frame is equal to or shorter than the available transmission timeperiod (step S604). Specifically, the control unit 17 determines whethera transmission time period of a data frame is equal to or shorter thanthe calculated available transmission time period.

When the transmission time period of a data frame is not equal to orshorter than the available transmission time period, the slave stationadjusts the transmission time period of a data frame to be equal to orshorter than the available transmission time period (step S605).Specifically, the data processing unit 11 performs fragmentation so thata transmission time period of any one part of a data frame obtained byfragmenting the data frame becomes equal to or shorter than theavailable transmission time period.

Next, the slave station generates a UL frame configured with an ACKframe of the received trigger frame and the data frame (step S606).Specifically, when the transmission time period of a data frame becomesequal to or shorter than the available transmission time period, thedata processing unit 11 generates a data frame and also generates an ACKframe of the trigger frame. Thereafter, the data processing unit 11generates a UL frame by connecting the data frame and the ACK frametogether.

Next, the slave station determines whether a transmission time period ofthe UL frame is shorter than the permitted transmission time period(step S607). Specifically, the data processing unit 11 determineswhether the transmission time period of the UL frame is shorter than thepermitted transmission time period.

When it is determined that the transmission time period of the UL frameis shorter than the permitted transmission time period, the slavestation inserts a padding into the UL frame (step S608). Specifically,when it is determined that the transmission time period of the UL frameis shorter than the permitted transmission time period, the dataprocessing unit 11 inserts paddings into the UL frame until thetransmission time period of the UL frame becomes the same as thepermitted transmission time period length.

Next, the slave station transmits the UL frame a predetermined timeafter reception of the trigger frame (step S609). Specifically, when thepredetermined time elapses after reception of the trigger frame, thecontrol unit 17 causes the communication unit 12 to transmit thegenerated UL frame to the master station.

(Frame Exchange Sequence in Present Embodiment)

Processing of the communication system in the present embodiment hasbeen described above. Next, transmission and reception of framesperformed in the communication system will be described with referenceto FIG. 9. FIG. 9 is a diagram showing an example of a frame exchangesequence performed by the communication system according to the presentembodiment.

First, a master station 10-1#0 transmits a TRQ frame to each of slavestations 10-1#1 to 10-1#4. For example, the TRQ frame is transmitted bybroadcasting, multicasting, or the like.

Next, each of the slave stations 10-1#1 to 10-1#4 transmits a TFB frameas a response to the TRQ frame. For example, as shown in FIG. 9, each ofTFB frames includes any one of training signal parts Training #1 toTraining #4 in which reference signals are positioned and RDRinformation. Here, the training signal parts are encoded.

Next, the master station 10-1#0 transmits trigger frames to therespective slave stations 10-1#1 to 10-1#4 using a space-divisionmultiplexing scheme. For example, each of the trigger frames includesany one of data parts DATA #01 to DATA #04 and RDG information as shownin FIG. 9.

Next, each of the slave stations 10-1#1 to 10-1#4 transmits a UL frameto the master station 10-1#0. For example, a UL frame of the slavestation 10-1#2 is configured with only an ACK frame and a data frame asshown in FIG. 9 because a requested transmission time period indicatedby RDR information in a TFB frame of the slave station 10-1#2 is themaximum. On the other hand, paddings are added to UL frames of the slavestations 10-1#1, 10-1#3, and 10-1#4 to compensate for the shortage of atransmission time period.

Next, the master station 10-1#0 transmits ACK frames of the received ULframes to the slave stations 10-1#1 to 10-1#4.

As described above, according to the first embodiment of the presentdisclosure, a master station receives frames including first informationfrom a plurality of slave stations, and transmits first frames includinginformation indicating a permitted transmission time period to theplurality of slave stations. Also, the master station determines thepermitted transmission time period on the basis of a plurality of piecesof the first information and generates the corresponding first frames.Thus, the permitted transmission time period suitable for situations ofthe slave stations is determined, and transmission time periods offrames to be transmitted are made the same as the correspondingpermitted transmission time period. In this way, it is possible toreconcile efficient use of wireless communication resources withstabilization of reception performance. Also, since the master stationside determines the permitted transmission time period and notifies theslave stations of the permitted transmission time period, a process ofdetermining a transmission time period is not performed on the slavestation side, and it is possible to achieve simplification of a processand power saving at the slave stations.

Also, the first information includes information indicating transmissiontime periods desired by the plurality of slave stations to be used fortransmission of user data. For this reason, the permitted transmissiontime period is directly determined in accordance with transmission timeperiods scheduled by the slave stations, so that a process ofdetermining a permitted transmission time period on the master stationside can be simplified.

Also, the transmission time periods are determined on the basis of theamount of data to be transmitted. For this reason, the permittedtransmission time period may be changed in accordance with the variableamount of transmission data, and thus it is possible to give flexibilityto a process of determining a permitted transmission time period.

Also, the master station determines the permitted transmission timeperiod on the basis of a transmission time period longer than othertransmission time periods among transmission time periods indicated byrespective pieces of the first information. For this reason, there is noexcess or deficiency of a transmission time period of a UL frame of aslave station which requests a longer transmission time period thanother slave stations, and thus it is possible to suppress the waste ofwireless communication resources to be used.

Also, the frames including the first information include referencesignals, and the master station transmits frames indicating transmissionrequests of frames including the first information to the plurality ofslave stations. For this reason, communication efficiency can beimproved by acquiring information for determining a permittedtransmission time period in a conventional process of exchanging TRQ/TFBframes.

Also, the frames including the first information are multiplexed byencoding the reference signals. For this reason, the respective slavestations can transmit TFB frames at the same timing, and it is possibleto shorten transmission time periods occupied by a process of exchangingTRQ/TFB frames and further reduce used wireless communication resources.

Also, the master station acquires antenna weights on the basis of thecorresponding reference signals, and transmits the first frames to theplurality of slave stations by space-division multiplexing the firstframes using the corresponding antenna weights. For this reason, triggerframes are transmitted at the same timing, and thus it is possible toimprove efficiency in frequency use and communication.

Also, according to the first embodiment of the present disclosure, theslave stations transmit the frames including the first information tothe master station and receive the first frames including theinformation indicating the permitted transmission time period determinedby the master station on the basis of a plurality of pieces of the firstinformation. Further, the slave stations generate frames on the basis ofthe information indicating the permitted transmission time period. Forthis reason, transmission time periods suitable for situations of theslave stations are determined, and thus it is possible to reconcilestabilization of reception power on the master station side withefficient use of wireless communication resources.

Also, the slave stations generate frames so that transmission timeperiods become the permitted transmission time period. For this reason,by making the transmission time periods of the frames transmitted fromthe slave stations the same as the permitted transmission time period,an abrupt change in reception power is suppressed during reception ofthe multiplexed frames at the master station, and it is possible tostabilize reception performance.

Also, the slave stations generate frames to which frames that areacknowledgements of the first frames are connected. For this reason,unlike a case in which an acknowledgement frame and a data frame areindependently transmitted, a transmission interval of each frame is notprovided, and it is possible to shorten a time period relating totransmission of both frames.

Also, when a transmission time period is shorter than the permittedtransmission time period, a slave station adds a padding to a frame. Forthis reason, even when it is difficult to make the transmission timeperiod the same as the permitted transmission time period with only adata frame, it is possible to stabilize reception performance.

2-3. Variations

The first embodiment of the present disclosure has been described above.Here, the present embodiment is not limited to the examples describedabove. First to third variations of the present embodiment will bedescribed below.

(First Variation)

In a first variation of the present embodiment, the master station maynot allow a slave station which requests a transmission time periodgreater than the threshold value to transmit a UL frame. Specifically,the control unit 17 controls the data processing unit 11 or thecommunication unit 12 so that a trigger frame is not transmitted to aslave station which is a transmission source of a frame including RDRinformation indicating a requested transmission time period greater thanthe threshold value.

For example, the control unit 17 may cause the data processing unit 11not to generate a trigger frame addressed to a slave station relating toa requested transmission time period greater than the threshold value,or to exclude the slave station relating to the requested transmissiontime period greater than the threshold value from destinations oftrigger frames. Also, the control unit 17 may cause the data processingunit 11 to generate a frame which does not include RDG informationindicating a permitted transmission time period instead of a triggerframe, and may not cause the communication unit 12 to transmit thegenerated frame.

As described above, according to the first variation of the presentembodiment, the control unit 17 controls the data processing unit 11 sothat a trigger frame is not transmitted to a slave station which is atransmission source of a frame including RDR information indicating arequested transmission time period greater than the threshold value. Forthis reason, when a permitted transmission time period shorter than arequested transmission time period is determined, a process of adjustinga UL frame to be transmitted is not provided in a slave station, and itis possible to simplify processing of the slave station.

(Second Variation)

In a second variation of the present embodiment, transmission power usedby slave stations to transmit UL frames may be controlled. Specifically,the data processing unit 11 includes information designatingtransmission power in trigger frames.

For example, the control unit 17 generates information designatingtransmission power for each slave station on the basis of receptionpower of respective frames previously received from the slave stations.Here, the information designating transmission power may be generatedfor only some of the plurality of slave stations.

Next, the data processing unit 11 includes the information designatingtransmission power used by the slave stations to transmit UL frames intrigger frames. Thereafter, the communication unit 12 transmits thetrigger frames generated by the data processing unit 11.

Slave stations which have received the trigger frames including theinformation designating transmission power set transmission power inaccordance with the corresponding information included in the triggerframes. Thereafter, the slave stations transmit UL frames to the masterstation using the set transmission power.

As described above, according to the second variation of the presentembodiment, the data processing unit 11 in the master station includesinformation designating transmission power used for frames transmittedfrom a plurality of slave stations to the master station in triggerframes. For this reason, the transmission power may be dynamicallychanged, and thus it is possible to stabilize reception performance ofthe master station.

Also, the transmission power is designated so that a difference inreception power between respective frames transmitted from a pluralityof other communication apparatuses to a communication apparatus is smallat the communication apparatus. For this reason, when transmission powervaries depending on a slave station, it is possible to preventtransmission waves for which transmission power lower than transmissionpower of other slave stations is used are weakened by transmission wavesof the other slave stations, and to prevent communication quality of aUL frame from being degraded.

Although an example in which a master station designates transmissionpower has been described above, a slave station may control transmissionpower even when no designation of transmission power is performed by themaster station. For example, the control unit 17 estimates propagationloss of transmission waves on the basis of previously acquiredinformation on reception power at the master station. Here, thereception power information may be included in a trigger frame.Subsequently, the control unit 17 sets transmission power on the basisof the estimated propagation loss so that reception power at the masterstation side becomes a predetermined value. Thereafter, thecommunication unit 12 transmits a UL frame to the master station usingthe set transmission power. In this case, communication for designatingtransmission power is not performed, and it is possible to use wirelesscommunication resources for other purposes or uses.

(Third Variation)

In a third variation of the present embodiment, the master station mayseparate space-division multiplexed UL frames using antenna weightsobtained from the corresponding UL frames. Specifically, the UL framesinclude reference signals, and the communication unit 12 separates thereference signals included in the received multiplexed UL frames.Thereafter, the data processing unit 11 calculates antenna weights fromthe separated reference signals, and the communication unit 12 separatesthe multiplexed UL frames using the calculated antenna weights. Here,the reference signals may be encoded using different orthogonal codes orthe like for different slave stations so that they are separable.

More specifically, the slave stations transmit UL frames includingreference signals encoded by an encoding method previously designated bythe master station due to a TRQ frame or the like to the master station.

In the master station, when the UL frames are received from the slavestations, the communication unit 12 separates the reference signals ofthe UL frames in accordance with the encoding method used by the slavestations. Subsequently, the data processing unit 11 calculates antennaweights on the basis of separated reference signals, and the controlunit 17 updates retained antenna weights, for example, antenna weightsat the time of the TRQ/TFB frame exchange described above, with thecalculated antenna weights. Thereafter, the communication unit 12separates the space-division multiplexed UL frames using the updatedantenna weights.

As described above, according to the third variation of the presentembodiment, a master station separates space-division multiplexed ULframes using antenna weights obtained from the corresponding UL frames.For this reason, even when antenna weights are not previously obtained,it is possible to separate space-division multiplexed frames. Also, evenwhen antenna weights can be previously acquired, it is possible toperform a process of separating frames using newer antenna weights, andit is possible to improve communication quality.

3. SECOND EMBODIMENT (EXAMPLE OF DIVIDING UL FRAME)

Communication apparatuses 10-1 according to the first embodiment of thepresent disclosure have been described above. Next, communicationapparatuses 10-2 according to a second embodiment of the presentdisclosure will be described. A slave station among communicationapparatuses 10-2 according to the present embodiment divides a UL frameinto an acknowledgement frame and a data frame and transmits each of thedivided frames to a master station in an independent transmission timeperiod.

3-1. Configuration of Communication Apparatus

A functional configuration of a communication apparatus 10-2 issubstantially the same as the functional configuration according to thefirst embodiment, but the data processing unit 11 and the control unit17 have partially different functions in both a master station and aslave station. Here, the description of functions which aresubstantially the same as functions of the first embodiment will beomitted.

((Functions of Case of Operating as Master Station))

First, functions of a case in which the communication station 10-2operates as a master station will be described in detail.

(Functions Relating to Uplink Transmission Time Period NotificationProcess)

The data processing unit 11 generates a TRQ frame for each slave stationwhich is a transmission destination. Specifically, the data processingunit 11 sets a destination of a TRQ frame as a single slave station andincludes only information which enables specifying of the single slavestation, for example, a single MAC address or the like, in the TRQframe. Here, unlike the first embodiment, the data processing unit 11may not include information indicating an encoding method for encoding areference signal of a TFB frame in the TRQ frame. This is for thepurpose of exchanging TRQ/TFB frames with each single slave station.

The control unit 17 performs a TRQ/TFB frame exchange process for eachtargeted slave station. Specifically, the control unit 17 causes thedata processing unit 11 to generate a TRQ frame for each slave stationwhich is a target of communication, and causes the communication unit 12to transmit the generated TRQ frame.

(Functions Relating to Uplink Multiplex Transmission Time PeriodDetermination Process)

When a slave station is instructed to divide a UL frame, the controlunit 17 determines two kinds of permitted transmission time periods.Specifically, when any one of TFB frames including RDR informationindicates that a slave station does not transmit a UL frame as aresponse to a trigger frame, the control unit 17 separately determinespermitted transmission time periods for an acknowledgement frame and aUL frame.

For example, the control unit 17 determines whether a requestedtransmission time period indicated by RDR information included in a TFBframe received from a slave station is 0 or a value corresponding to 0.When it is determined that the requested transmission time period is 0or a value corresponding to 0, the control unit 17 determines apermitted transmission time period of an ACK frame to be T_(ack) anddetermines a permitted transmission time period of a UL frame on thebasis of an expression R_(max)+T_(IFS)+T_(ack). Here, T_(IFS) indicatesa transmission interval inter-frame space (IFS) between the ACK frameand a follow-up data frame. Here, information indicating the permittedtransmission time period of the ACK frame is also referred to as RDG₀,and information indicating the permitted transmission time period of theUL frame is also referred to as RDG₁.

Also, when a threshold value is provided for a permitted transmissiontime period, the control unit 17 may determine the permittedtransmission time period of the UL frame on the basis of an expressionmin(G_(limit), R_(max)+T_(IFS)+T_(ack)).

(Functions Relating to Uplink Multiplex Transmission and ReceptionProcess)

The data processing unit 11 includes information instructing division ofa UL frame transmitted by a slave station in a trigger frame.Specifically, when any one of TFB frames including RDR informationindicates that a slave station does not transmit a UL frame as aresponse to a trigger frame, the data processing unit 11 includesinformation instructing transmission of an acknowledgement frame of atrigger frame in an independent transmission time period in the triggerframe.

For example, a trigger frame may include a flag Split_Ack_Flag as theinformation instructing transmission of an acknowledgement frame of thetrigger frame in an independent transmission time period. The dataprocessing unit 11 determines whether a requested transmission timeperiod indicated by RDR information included in a TFB frame receivedfrom a slave station is 0 or a value corresponding to 0. When it isdetermined that the requested transmission time period is 0 or a valuecorresponding to 0, the data processing unit 11 may insert a flag whichis turned on, in other words, Split_Ack_Flag=1, at a predeterminedposition in a trigger frame, for example, a part of a reserved area in aMAC header. Here, an insertion position of the corresponding flag is notlimited thereto. For example, another dedicated field may be added tothe trigger frame, and the corresponding flag may be inserted into theadded field.

Although an example in which a flag is included in a trigger frame whena requested transmission time period is 0 has been described above, whena TFB frame including RDR information indicating a requestedtransmission time period is not received, the data processing unit 11may include the corresponding flag in a trigger frame.

Also, the data processing unit 11 includes information indicating twokinds of permitted transmission time periods in a trigger frame.Specifically, the data processing unit 11 includes RDG informationindicating a permitted transmission time period of an ACK frame and apermitted transmission time period of a UL frame determined by thecontrol unit 17 in a trigger frame.

Here, when the permitted transmission time period of an ACK frame isknown to a slave station, the data processing unit 11 may not includeinformation indicating the permitted transmission time period of an ACKframe in a trigger frame. Also, the data processing unit 11 may notinclude the permitted transmission time period of a UL frame in atrigger frame relating to a slave station whose requested transmissiontime period is 0.

((Functions of Case of Operating as Slave Station))

Next, functions of a case in which the communication station 10-2operates as a slave station will be described in detail.

(Functions Relating to Uplink Transmission Time Period NotificationProcess)

Since the data processing unit 11 has substantially the same functionsas that in the first embodiment except that a reference signal includedin a TFB frame is not encoded, the description thereof will be omitted.

When there is no data to be transmitted, the control unit 17 determinesa requested transmission time period to be 0. Specifically, when thereis no data to be transmitted in a transmission buffer, the control unit17 determines a requested transmission time period to be 0 or a valuecorresponding to 0. Here, when there is no data to be transmitted, thecontrol unit 17 may perform control so that the data processing unit 11does not generate a TFB frame or the communication unit 12 does nottransmit a TFB frame. Also, when there is no data to be transmitted, thecontrol unit 17 may cause the data processing unit 11 to generate a TFBframe including information indicating that there is no data to betransmitted, no UL frame is transmitted, or the like.

(Functions Relating to Uplink Multiplex Transmission and ReceptionProcess)

When information instructing division of a UL frame is included in atrigger frame, the data processing unit 11 divides the UL frame.Specifically, when information instructing transmission of anacknowledgement of a trigger frame in an independent transmission timeperiod is included in a trigger frame, the data processing unit 11generates a frame as the corresponding acknowledgement which isindependently transmitted.

For example, when a trigger frame is received, the data processing unit11 determines whether a flag is included or content of a flag ispredetermined content, for example, that the flag is turned on, in otherwords, Split_Ack_Flag=1. When it is determined that the flag is turnedon, the data processing unit 11 generates an ACK frame of the triggerframe on the basis of a permitted transmission time period of an ACKframe.

Next, the data processing unit 11 determines whether there is data to betransmitted, in other words, a requested transmission time periodindicated by RDR information included in a TFB frame is 0. When it isdetermined that there is data to be transmitted, the data processingunit 11 generates a data frame on the basis of a permitted transmissiontime period of a UL frame. At this time, the data frame is generated inconsideration of the transmission interval T_(IFS) between an ACK frameand a data frame. Also, when it is determined that there is no data tobe transmitted, a data frame is neither generated nor transmitted.

When a UL frame is divided, the control unit 17 causes the communicationunit 12 to transmit each of divided frames in a permitted transmissiontime period of each divided frame. Specifically, when both of an ACKframe and a data frame are separately generated, the control unit 17causes the communication unit 12 to first transmit only the ACK frame toa master station in the same transmission time period as other slavestations, in other words, in the permitted transmission time period ofan ACK frame. Also, when a predetermined transmission interval elapsesafter transmission of the corresponding ACK frame, the control unit 17causes the communication unit 12 to transmit the data frame to themaster station in a permitted transmission time period.

Although an example in which an ACK frame is transmitted in advance of adata frame has been described above, an ACK frame may be transmittedafter a data frame.

3-2. Processing of Communication Apparatus

Next, processing of the communication stations 10-1 according to thepresent embodiment will be described with reference to FIGS. 10 to 12.Here, only processes different from those of the first embodiment willbe described.

(Flow of Uplink Transmission Time Period Notification Process)

First, processing of a master station in an uplink transmission timeperiod notification process will be described with reference to FIG. 10.FIG. 10 is a flowchart conceptually showing processing of a masterstation in an uplink transmission time period notification processaccording to the present embodiment.

First, a master station generates a TRQ frame (step S211). Specifically,the data processing unit 11 generates a TRQ frame including informationindicating a single slave station which is a destination of the TRQframe. Here, unlike the first embodiment, information indicating amethod of encoding a reference signal is not included in the TRQ frame.

Next, the master station transmits the TRQ frame (step S212), anddetermines whether a TFB frame has been received within a predeterminedtime (step S213).

When it is determined that no TFB frame has been received within thepredetermined time, the master station determines whether the number ofretransmissions of the TRQ frame is equal to or smaller than apredetermined number of times (step S214), and retransmits the TRQ framewhen the corresponding number of retransmissions is equal to or smallerthan the predetermined number of times.

When it is determined that TFB frames have been received within thepredetermined time, the master station determines whether the TFB frameshave been received from all of transmission-target stations of triggerframes (step S215). Specifically, the control unit 17 determines whetherTFB frames have been received from all transmission-target stations oftrigger frames on the basis of past reception results of TFB frames.When it is determined that the TFB frames have not been received fromall of the transmission-target stations of trigger frames, the controlunit 17 returns to step S211 or step S212 and transmits a TRQ frame to aslave station from which no TFB frame has been received.

(Flow of Uplink Multiplex Transmission Time Period DeterminationProcess)

An uplink multiplex transmission time period determination process willbe described next with reference to FIG. 11. FIG. 11 is a flowchartconceptually showing processing of a master station performing an uplinkmultiplex transmission time period determination process according tothe present embodiment.

First, the master station acquires an antenna weight and a requestedtransmission time period from each TFB frame (step S411), and specifiesa maximum value among the acquired requested transmission time periods(step S412).

Next, the master station determines whether there is a threshold valueof a permitted transmission time period (step S413), and determines apermitted transmission time period on the basis of the maximum value ofrequested transmission time periods and an ACK transmission time period(step S414) when it is determined that there is no threshold value of apermitted transmission time period. Specifically, the control unit 17determines whether there is a threshold value of a permittedtransmission time period, and determines RDG₀ information indicating apermitted transmission time period of ACK frames and RDG₁ informationindicating a transmission time period of data frames.

Also, when it is determined that there is a threshold value of apermitted transmission time period, the master station determines apermitted transmission time period on the basis of the maximum value ofrequested transmission time periods, the ACK transmission time period,and the threshold value (step S415).

Next, the master station determines whether there is a TFB frame whoserequested transmission time period is 0 (step S416). Specifically, thecontrol unit 17 determines whether there is a TFB frame in which RDRinformation indicates a requested transmission time period of 0 or avalue corresponding to 0.

When it is determined that there is a TFB frame whose requestedtransmission time period is 0, the master station determines to turn ona flag (step S417), and in the opposite case, the master stationdetermines to turn off the flag (step S418). Specifically, when it isdetermined by the control unit 17 that there is a TFB frame whoserequested transmission time period is 0 or a value corresponding to 0,the data processing unit 11 inserts a flag whose value is on, in otherwords, Split_Ack_Flag=1, into a trigger frame. In the opposite case, thedata processing unit 11 inserts a flag whose value is off, in otherwords, Split_Ack_Flag=0, into the trigger frame.

(Flow of Uplink Multiplex Transmission and Reception Process)

An uplink multiplex transmission and reception process will be describednext with reference to FIG. 12. FIG. 12 is a flowchart conceptuallyshowing processing of a slave station performing an uplink multiplextransmission and reception process according to the present embodiment.

First, the master station waits until a trigger frame is received (stepS611). When a trigger frame is received, the master station acquires aflag and a permitted transmission time period from the correspondingtrigger frame (step S612). Specifically, the data processing unit 11acquires a flag Split_Ack_Flag and RDG information indicating apermitted transmission time period from the trigger frame.

Next, the master station determines whether the flag is turned on (stepS613), and transmits an ACK frame on the basis of an ACK transmissiontime period of the permitted transmission time period (step S614) whenit is determined that the flag is turned on. Specifically, the dataprocessing unit 11 determines whether the acquired flag is turned on, inother words, Split_Ack_Flag=1. When it is determined that the flag isturned on, the data processing unit 11 generates only an ACK frame, andthe control unit 17 causes the communication unit 12 to transmit the ACKframe in the permitted transmission time period T_(ack) of an ACK frame.Also, since processing (steps S617 to S620) of a case in which it isdetermined that the flag is turned off is substantially the same as theprocess of the first embodiment, the description thereof will beomitted.

Next, the master station determines whether there is a data frame (stepS615). When there is a data frame, the master station generates a ULframe on the basis of the data frame (step S616). Specifically, the dataprocessing unit 11 determines whether there is data to be transmittedwith reference to a transmission buffer or the like, and generates adata frame when there is data. Thereafter, when there is a data frame,the control unit 17 causes the communication unit 12 to transmit thecorresponding data frame after lapse of a permitted transmission timeperiod of a UL frame, for example, the period R_(max)+T_(IFS)+T_(ack).

Next, the master station determines whether a transmission time periodof the UL frame is shorter than the permitted transmission time period(step S621), and inserts a padding into the UL frame (step S622) when itis determined that the corresponding transmission time period is shorterthan the permitted transmission time period.

Next, the master station transmits the UL frame (step S623).Specifically, when the flag is turned on, the control unit 17 causes thecommunication unit 12 to transmit the UL frame a predetermined timeafter transmission of the ACK frame. Also, when the flag is turned off,the control unit 17 causes the communication unit 12 to transmit a ULframe configured with the ACK frame and the data frame a predeterminedtime after transmission of the trigger frame.

(Frame Exchange Sequence in Present Embodiment)

Processing of the communication system according to the presentembodiment has been described above. Next, transmission and reception offrames performed in the communication system will be described withreference to FIG. 13. FIG. 13 is a diagram showing an example of a frameexchange sequence performed by a communication system according to thepresent embodiment. Here, the description of portions which aresubstantially the same as those of the first embodiment will be omitted.

First, a master station 10-2#0 transmits a TRQ frame to a slave station10-2#1. For example, the TRQ frame is transmitted by unicasting or thelike, and the slave station 10-2#1 transmits a TFB frame as a responseto the TRQ frame. This TRQ/TFB frame exchange is performed with each ofother slave stations 10-2#2 to 10-2#4.

Next, the master station 10-2#0 transmits trigger frames to therespective slave stations 10-2#1 to 10-2#4 using space-divisionmultiplexing.

Next, each of the slave stations 10-2#1 to 10-2#4 transmits an ACK frameto the master station 10-2#0 first. Thereafter, when a predeterminedtime elapses, the slave stations 10-2#1 and 10-2#2 continuously transmitUL frames of only data frames to the master station, and the slavestations 10-2#3 and 10-2#4 do not transmit subsequent UL frames. This isbecause the slave stations 10-2#3 and 10-2#4 do not have data to betransmitted.

Next, the master station 10-2#0 transmits ACK frames of the received ULframes to the slave stations 10-2#1 and 10-2#2.

As described above, according to the second embodiment of the presentdisclosure, when any one of frames including first information indicatesthat a slave station does not transmit a UL frame as a response to atrigger frame, a master station includes information instructingtransmission of an acknowledgement of the trigger frame in anindependent transmission time period in a first frame.

Here, when permitted transmission time periods are uniformly determinedfor all slave stations which are targets of communication, a slavestation having no data to be transmitted inserts a padding at a positionat which a data frame is inserted, and a useless transmission timeperiod lengthens, in other words, power is wasted. On the other hand,according to the present embodiment, a slave station having no data tobe transmitted may transmit only an ACK frame, and a transmission timeperiod is optimized, so that power consumption at the slave station canbe reduced.

Also, information indicating a common transmission time period isincluded in information indicating a permitted transmission time period.For this reason, even when a transmission time period of an ACK framethat can be allocated to a slave station varies, the slave station cancope with the corresponding variation, and it is possible to increaseflexibility with respect to a change of a communication situation.

3-3. Variations

The second embodiment of the present disclosure has been describedabove. Note that this embodiment is not limited to the above examples.Variations of this embodiment will now be described.

In a variation of the present embodiment, even when a slave stationindicates that no UL frame is transmitted as a response to a triggerframe, the slave station may transmit a UL frame. Specifically, if aslave station needs to transmit a UL frame after indicating that no ULframe is transmitted as a response to a trigger frame, when a frameincluding information indicating a permitted transmission time period isreceived, the slave station transmits the UL frame in the correspondingpermitted transmission time period.

For example, in the slave station, the data processing unit 11 generatesa TFB frame including information indicating that a requestedtransmission time period is 0 or a value corresponding to 0, and thecorresponding TFB frame is transmitted to a master station by thecommunication unit 12.

The master station that has received the corresponding TFB framedetermines a permitted transmission time period on the basis ofrequested transmission time periods of other slave stations, andtransmits a trigger frame including information indicating thedetermined permitted transmission time period to the slave station.

When the corresponding trigger frame is received by the slave stationand data to be transmitted is generated after transmission of the TFBframe, the data processing unit 11 generates a UL frame on the basis ofinformation indicating the permitted transmission time period includedin the corresponding trigger frame. Thereafter, the control unit 17transmits the UL frame in the corresponding permitted transmission timeperiod.

As described above, according to the variation of the presentembodiment, if a slave station needs to transmit a UL frame afterindicating that no UL frame is transmitted as a response to a triggerframe, when a frame including information indicating a permittedtransmission time period is received, the slave station transmits the ULframe in the corresponding permitted transmission time period. For thisreason, even when a generation time point of data to be transmitted anda transmission time point of a TFB frame are out of sequence, the slavestation is enabled to transmit data while the slave station is set as atarget of transmission. Therefore, it is possible to reduce waiting timefor allocation of wireless communication resources and improvecommunication efficiency.

4. THIRD EMBODIMENT (EXAMPLE OF MULTICAST COMMUNICATION)

Communication apparatuses 10-2 according to the second embodiment of thepresent disclosure have been described above. Next, communicationapparatuses 10-3 according to a third embodiment of the presentdisclosure will be described. A master station among communicationapparatuses 10-3 according to the present embodiment transmits a triggerframe using a multicast scheme.

4-1. Configuration of Communication Apparatus

A functional configuration of a communication apparatus 10-3 issubstantially the same as the functional configuration according to thefirst or second embodiment, but the data processing unit 11 and thecontrol unit 17 have partially different functions in a master station.Here, the description of functions which are substantially the same asfunctions of the first or second embodiment will be omitted.

((Functions Relating to Uplink Multiplex Transmission and ReceptionProcess))

The data processing unit 11 generates one frame including informationindicating a permitted transmission time period. Specifically, the dataprocessing unit 11 does not generate a trigger frame including RDGinformation for each slave station which is a target of transmission,but generates one trigger frame.

The control unit 17 causes the communication unit 12 to transmit thetrigger frame using a multicast scheme.

4-2. Processing of Communication Apparatus

Processing of the communication apparatuses 10-3 in the communicationsystem according to the present embodiment is substantially the same asprocessing in the first or second embodiment except that a method oftransmitting a trigger frame in the uplink multiplex transmission andreception process is changed from space-division multiplexing tomulticasting. For this reason, processing of the present embodiment willbe schematically described using a frame exchange sequence.

(Frame Exchange Sequence in Present Embodiment)

Transmission and reception of frames performed in the communicationsystem according to the present embodiment will be described withreference to FIG. 14. FIG. 14 is a diagram showing an example of a frameexchange sequence performed by a communication system according to thepresent embodiment. Here, the description of portions which aresubstantially the same as those of the first or second embodiment willbe omitted.

First, a master station 10-3#0 transmits a TRQ frame to each of slavestations 10-3#1 to 10-3#4, and each of the slave stations 10-3#1 to10-3#4 transmits a TFB frame as a response to the TRQ frame.

Next, the master station 10-3#0 transmits a trigger frame to each of theslave stations 10-3#1 to 10-3#4 using a multicast scheme. For example,one trigger frame is generated, and the slave stations 10-3#1 to 10-3#4are designated as destinations.

Next, each of the slave stations 10-3#1 to 10-3#4 transmits a UL frameto the master station 10-3#0, and the master station 10-3#0 transmitsACK frames of the received UL frames to the slave stations 10-3#1 to10-3#4.

As described above, according to the third embodiment of the presentdisclosure, a master station transmits a trigger frame to a plurality ofslave stations using a multicast scheme. For this reason, in comparisonwith a case of space-division multiplexing trigger frames, aspace-division multiplexing process is omitted, and thus it is possibleto simplify a process involved in transmission of trigger frames.

5. FOURTH EMBODIMENT (EXAMPLE OF FREQUENCY-DIVISION MULTIPLEXCOMMUNICATION)

The communication apparatus 10-3 according to the third embodiment ofthe present disclosure has been described above. Next, a communicationapparatus 10-4 according to a fourth embodiment of the presentdisclosure will be described. The communication apparatus 10-4 accordingto this embodiment perform communication using a frequency-divisionmultiplexing scheme instead of a space-division multiplexing scheme.

5-1. Configuration of Communication Apparatus

The communication apparatus 10-4 has substantially the same functionalconfiguration as that of the first to third embodiments, however, in themaster station, it has partially different functions of the dataprocessing unit 11, the communication unit 12, and the control unit 17.Note that substantially the same functions as those of the first tothird embodiments will not be described.

((Basic Functions))

The modulation/demodulation unit 13 and the signal processing unit 14 inthe communication unit 12 perform a process involved infrequency-division multiplexing. Specifically, themodulation/demodulation unit 13 divides a frame provided from the dataprocessing unit 11 into portions, the number of which is equal to thenumber of subcarriers, and modulates each portion of the frame obtainedby the division. Thereafter, the modulation/demodulation unit 13combines signals obtained by the modulation, and provides the signalobtained by the combination to the signal processing unit 14. The signalprocessing unit 14 performs a process, such as addition of a guardinterval, or the like, on the signal provided from themodulation/demodulation unit 13, and provides a signal obtained by theprocess, i.e., a symbol stream, to the radio interface unit 16.

The signal processing unit 14 performs a process, such as removal of aguard interval, or the like, on the symbol stream related to receivedwaves provided from the radio interface unit 16, and provides a signalobtained by the process to the modulation/demodulation unit 13. Themodulation/demodulation unit 13 extracts a subcarrier signal from thesignal provided from the signal processing unit 14, and demodulates eachsubcarrier. Thereafter, the modulation/demodulation unit 13 combinesframes obtained by the demodulation, and provides the combined frame tothe data processing unit 11.

Here, functions of the data processing unit 11 and the control unit willbe described together with processing of the communication apparatuses10-4.

5-2. Processing of Communication Apparatus

Next, processing of the communication system and the communicationstations 10-4 in the present embodiment will be described with referenceto FIGS. 6 to 8. Here, since processes shown in FIGS. 4 and 5 aresubstantially the same as those of the first embodiment, the descriptionthereof will be omitted.

(Flow of Uplink Multiplex Transmission Time Period DeterminationProcess)

An uplink multiplex transmission time period determination process inthe present embodiment will be described in detail with reference toFIG. 6.

First, the master station acquires a frequency and a requestedtransmission time period from each TFB frame (step S401). Specifically,the data processing unit 11 acquires information indicating subcarriersallocated to slave stations and requested transmission time periods fromTFB frames.

Next, the master station specifies a maximum value among the acquiredrequested transmission time periods (step S402), and determines whetherthere is a threshold value of a permitted transmission time period (stepS403).

When it is determined that there is no threshold value of a permittedtransmission time period, the master station determines a permittedtransmission time period on the basis of the maximum value of requestedtransmission time periods and an ACK transmission time period (stepS404). Specifically, the control unit 17 determines the sum of themaximum value R_(max) of requested transmission time periods and the ACKtransmission time period T_(ack) as a permitted transmission timeperiod.

Here, the control unit 17 determines the permitted transmission timeperiod to be a value corresponding to frequency-division multiplexing.Specifically, the control unit 17 applies effects of degradation of adata rate caused by frequency-division multiplexing to a permittedtransmission time period. For example, when the requested transmissiontime periods are values obtained without assuming that frames to betransmitted are frequency-division multiplexed, the control unit 17multiplies the requested transmission time periods by a valuecorresponding to a frequency division number. For example, when afrequency band is quartered and allocated to respective slave stations,a data rate of each slave station is quartered, and thus a valueobtained by multiplying a requested transmission time period by four isused to determine a permitted transmission time period.

When it is determined that there is a threshold value of a permittedtransmission time period, the master station determines a permittedtransmission time period on the basis of the maximum value of requestedtransmission time periods, the ACK transmission time period, and thethreshold value (step S405).

(Flow of Uplink Multiplex Transmission and Reception Process)

An uplink multiplex transmission and reception process in the presentembodiment will be described in detail next. First, processing of themaster station in the uplink multiplex transmission and receptionprocess will be described with reference to FIG. 7.

First, the master station generates trigger frames including informationindicating the permitted transmission time period (step S501), andtransmits the trigger frames which are frequency-division multiplexed(step S502). Specifically, the communication unit 12 modulates andmultiplexes respective trigger frames generated by the data processingunit 11 using different subcarriers and transmits the multiplexedtrigger frames. Here, the data processing unit 11 includes subcarrierinformation indicating the subcarriers allocated to the respective slavestations in the trigger frames. For example, the subcarrier informationmay be inserted into a PHY header portion. It is assumed that a PHYheader is modulated using an entire frequency band. Also, the slavestations may be previously notified of the subcarrier information, orthe subcarrier information may be fixed for each slave station. Here, anexample in which subcarrier information relating to multiplexing(downlink multiplexing) of the corresponding trigger frames andsubcarrier information relating to multiplexing (uplink multiplexing) ofUL frames transmitted as responses to the corresponding trigger framesare the same has been described, but these pieces of subcarrierinformation may be different. In this case, the slave stations areseparately notified of respective pieces of the subcarrier informationrelating to downlink multiplexing and uplink multiplexing.

Next, the master station determines whether UL frames have been receivedwithin a predetermined time (step S503). Specifically, the communicationunit 12 waits the predetermined time to receive UL frames. At this time,the communication unit 12 performs a process of separating UL framesusing the subcarriers indicated by the subcarrier information includedin the trigger frames. Also, even before the transmission of the triggerframes, the communication unit 12 may retain the subcarrier informationof which the slave stations have been notified, and perform the processof separating the UL frames using the corresponding subcarrierinformation. Here, when the subcarrier information relating to downlinkmultiplexing and the subcarrier information transmitted as responses tothe trigger frames and relating to uplink multiplexing are different,the corresponding separation process is performed on the basis of thesubcarrier information relating to uplink multiplexing.

When it is determined that UL frames have been received within thepredetermined time, the master station transmits ACK frames of thereceived UL frames (step S505). Specifically, the communication unit 12performs a process for frequency-division multiplexing generated ACKframes using the retained subcarrier information and transmits theprocessed ACK frames to the slave stations.

When it is determined that UL frames have not been received within thepredetermined time, the master station determines whether the number ofretransmissions of the trigger frames is equal to or smaller than apredetermined number of times (step S505).

Processing of a slave station in the uplink multiplex transmission andreception process according to the present embodiment will be describednext with reference to FIG. 8.

First, a slave station waits until a trigger frame is received (stepS601). When a trigger frame is received, the slave station acquires thepermitted transmission time period from the corresponding trigger frame(step S602). Specifically, the communication unit 12 acquires thesubcarrier information from the received trigger frame. For example, thecommunication unit 12 acquires subcarrier information indicating asubcarrier addressed to the slave station from a PHY header of thetrigger frame. Thereafter, the communication unit 12 performs a framedemodulation process and the like on the subcarrier indicated by thecorresponding subcarrier information. Also, the corresponding subcarrierinformation is retained to be used in a post-stage process. Here, whenthe subcarrier information relating to downlink multiplexing and thesubcarrier information relating to uplink multiplexing are different,the subcarrier information relating to downlink multiplexing is used inthe corresponding demodulation process and the like, and the subcarrierinformation relating to uplink multiplexing is retained to be used in apost-stage process.

Next, the slave station performs the process of steps S603 to S609.Here, a transmission time period in the corresponding process is handledas a value in which frequency-division multiplexing has been taken intoconsideration.

Also, a frame exchange sequence in the present embodiment issubstantially the same as that of the first embodiment, and thus thedescription thereof will be omitted.

As described above, according to the fourth embodiment of the presentdisclosure, a master station frequency-division multiplexes first framesand transmits the multiplexed first frames to a plurality of slavestations. For this reason, even an apparatus and the like conforming toa wireless communication standard which does not support aspace-division multiplexing scheme is included among applicationtargets, and thus it is possible to further improve communicationefficiency.

6. APPLICATION EXAMPLE

The technology according to the embodiments of the disclosure can beapplied to various products. For example, the communication apparatus 10may be realized as mobile terminals such as smartphones, tablet PCs(Personal Computers), notebook PCs, portable game terminals, or digitalcameras, fixed-type terminals such as television receivers, printers,digital scanners, or network storages, or car-mounted terminals such ascar navigation devices. In addition, the communication apparatus 10 maybe realized as terminals that perform M2M (Machine to Machine)communication (also referred to as MTC (Machine Type Communication)terminals) such as smart meters, vending machines, remotely controlledsurveillance devices, or POS (Point Of Sale) terminals. Furthermore, thecommunication apparatus 10 may be wireless communication modules mountedin such terminals (for example, integrated circuit modules configured byone die).

On the other hand, for example, the master station of the communicationapparatus 10 may be realized as a wireless LAN access point (alsoreferred to as a wireless base station) which has a router function ordoes not have a router function. The master station of the communicationapparatus 10 may be realized as a mobile wireless LAN router. The masterstation of the communication apparatus 10 may also be a wirelesscommunication module (for example, an integrated circuit moduleconfigured with one die) mounted on the device.

6-1. First Application Example

FIG. 15 is a block diagram showing an example of a schematicconfiguration of a smartphone 900 to which the technology of the presentdisclosure can be applied. The smartphone 900 includes a processor 901,a memory 902, a storage 903, an externally connected interface 904, acamera 906, a sensor 907, a microphone 908, a input device 909, adisplay device 910, a speaker 911, a wireless communication interface913, an antenna switch 914, an antenna 915, a bus 917, a battery 918,and an auxiliary controller 919.

The processor 901 may be, for example, a CPU (Central Processing Unit)or an SoC (System on Chip), and controls functions of an applicationlayer and other layers of the smartphone 900. The memory 902 includes aRAM (Random Access Memory) and a ROM (Read Only Memory), and storesprograms executed by the processor 901 and data. The storage 903 caninclude a storage medium such as a semiconductor memory or a hard disk.The externally connected interface 904 is an interface for connecting anexternally attached device such as a memory card or a USB (UniversalSerial Bus) device to the smartphone 900.

The camera 906 has an image sensor, for example, a CCD (Charge CoupledDevice) or a CMOS (Complementary Metal Oxide Semiconductor), to generatecaptured images. The sensor 907 can include a sensor group including,for example, a positioning sensor, a gyro sensor, a geomagnetic sensor,an acceleration sensor, and the like. The microphone 908 converts soundsinput to the smartphone 900 into audio signals. The input device 909includes, for example, a touch sensor that detects touches on a screenof the display device 910, a key pad, a keyboard, buttons, switches, andthe like, to receive manipulations or information inputs from a user.The display device 910 has a screen such as a liquid crystal display(LCD), or an organic light emitting diode (OLED) display to displayoutput images of the smartphone 900. The speaker 911 converts audiosignals output from the smartphone 900 into sounds.

The wireless communication interface 913 supports one or more wirelessLAN standards of IEEE 802.11a, 11g, 11n, 11ac, and 11ad, to execute thewireless LAN communication. The wireless communication interface 913 cancommunicate with another device via a wireless LAN access point in aninfrastructure mode. In addition, the wireless communication interface913 can directly communicate with another device in a directcommunication mode such as an ad hoc mode or Wi-Fi Direct (registeredtrademark). Wi-Fi Direct is different from the ad hoc mode, and thus oneof two terminals operates as an access point. However, communication isperformed directly between the terminals. The wireless communicationinterface 913 can typically include a baseband processor, an RF (RadioFrequency) circuit, a power amplifier, and the like. The wirelesscommunication interface 913 may be a single-chip module on which amemory that stores a communication control program, a processor thatexecutes the program, and a relevant circuit are integrated. Thewireless communication interface 913 may support another kind ofwireless communication scheme such as a cellular communication scheme, ashort-range wireless communication scheme, or a proximity wirelesscommunication scheme in addition to the wireless LAN scheme. The antennaswitch 914 switches a connection destination of the antenna 915 for aplurality of circuits (for example, circuits for different wirelesscommunication schemes) included in the wireless communication interface913. The antenna 915 has a single or a plurality of antenna elements(for example, a plurality of antenna elements constituting a MIMOantenna), and is used for transmission and reception of wireless signalsfrom the wireless communication interface 913.

Note that the smartphone 900 may include a plurality of antennas (forexample, antennas for a wireless LAN or antennas for a proximitywireless communication scheme, or the like), without being limited tothe example of FIG. 15. In this case, the antenna switch 914 may beomitted from the configuration of the smartphone 900.

The bus 917 connects the processor 901, the memory 902, the storage 903,the externally connected interface 904, the camera 906, the sensor 907,the microphone 908, the input device 909, the display device 910, thespeaker 911, the wireless communication interface 913, and the auxiliarycontroller 919 to one another. The battery 918 supplies electric powerto each of the blocks of the smartphone 900 shown in FIG. 15 via powersupply lines partially indicated by dashed lines in the drawing. Theauxiliary controller 919 causes, for example, necessary minimumfunctions of the smartphone 900 to be operated in a sleep mode.

In the smartphone 900 shown in FIG. 15, the data processing unit 11, thecommunication unit 12, and the control unit 17 described with referenceto FIG. 2 may be mounted in the wireless communication interface 913. Atleast some of the functions may be mounted on the processor 901 or theauxiliary controller 919. For example, the control unit 17 determines apermitted transmission time period on the basis of received requestedtransmission time periods, so that communication efficiency can beimproved.

Note that the smartphone 900 may operate as a wireless access point(software AP) as the processor 901 executes the function of an accesspoint at an application level. In addition, the wireless communicationinterface 913 may have the function of a wireless access point.

6-2. Second Application Example

FIG. 16 is a block diagram showing an example of a schematicconfiguration of a car navigation device 920 to which the technology ofthe present disclosure can be applied. The car navigation device 920includes a processor 921, a memory 922, a GPS (Global PositioningSystem) module 924, a sensor 925, a data interface 926, a content player927, a storage medium interface 928, an input device 929, a displaydevice 930, a speaker 931, a wireless communication interface 933, anantenna switch 934, an antenna 935, and a battery 938.

The processor 921 may be, for example, a CPU or an SoC controlling anavigation function and other functions of the car navigation device920. The memory 922 includes a RAM and a ROM storing programs executedby the processor 921 and data.

The GPS module 924 measures a position of the car navigation device 920(for example, latitude, longitude, and altitude) using GPS signalsreceived from a GPS satellite. The sensor 925 can include a sensor groupincluding, for example, a gyro sensor, a geomagnetic sensor, a pneumaticsensor, and the like. The data interface 926 is connected to anin-vehicle network 941 via, for example, a terminal that is notillustrated to acquire data generated on the vehicle side such as carspeed data.

The content player 927 reproduces content stored in a storage medium(for example, a CD or a DVD) inserted into the storage medium interface928. The input device 929 includes, for example, a touch sensor thatdetects touches on a screen of the display device 930, buttons,switches, and the like to receive manipulations or information inputsfrom a user. The display device 930 has a screen such as an LCD or anOLED display to display images of the navigation function or reproducedcontent. The speaker 931 outputs sounds of the navigation function orreproduced content.

The wireless communication interface 933 supports one or more wirelessLAN standards of IEEE 802.11a, 11g, 11n, 11ac, and 11ad, to executewireless LAN communication. The wireless communication interface 933 cancommunicate with another device via a wireless LAN access point in theinfrastructure mode. In addition, the wireless communication interface933 can directly communicate with another device in a directcommunication mode such as an ad hoc mode or Wi-Fi Direct. The wirelesscommunication interface 933 can typically have a baseband processor, anRF circuit, a power amplifier, and the like. The wireless communicationinterface 933 may be a single-chip module on which a memory that storesa communication control program, a processor that executes the program,and a relevant circuit are integrated. The wireless communicationinterface 933 may support another kind of wireless communication schemesuch as a short-range wireless communication scheme, a proximitywireless communication scheme, or the cellular communication scheme inaddition to the wireless LAN scheme. The antenna switch 934 switches aconnection destination of the antenna 935 for a plurality of circuitsincluded in the wireless communication interface 933. The antenna 935has a single or a plurality of antenna elements and is used fortransmission and reception of wireless signals from the wirelesscommunication interface 933.

Note that the car navigation device 920 may include a plurality ofantennas, without being limited to the example of FIG. 16. In this case,the antenna switch 934 may be omitted from the configuration of the carnavigation device 920.

The battery 938 supplies electric power to each of the blocks of the carnavigation device 920 shown in FIG. 16 via power supply lines partiallyindicated by dashed lines in the drawing. In addition, the battery 938accumulates electric power supplied from the vehicle.

In the car navigation device 920 shown in FIG. 16, the data processingunit 11, the communication unit 12, and the control unit 17 describedwith reference to FIG. 2 may be mounted in the wireless communicationinterface 933. At least some of the functions may be mounted on theprocessor 921. For example, the control unit 17 determines a permittedtransmission time period on the basis of received requested transmissiontime periods, so that communication efficiency can be improved.

In addition, the wireless communication interface 933 may operate as thecommunication apparatus 10 described above and provide wirelessconnection to a terminal owned by a user who is riding in a vehicle. Atthis time, for example, it is possible to increase communication speedbetween the terminal owned by the user and the car navigation device920.

The technology of the present disclosure may be realized as anin-vehicle system (or a vehicle) 940 including one or more blocks of theabove-described car navigation device 920, an in-vehicle network 941,and a vehicle-side module 942. The vehicle-side module 942 generatesvehicle-side data such as a vehicle speed, the number of enginerotations, or failure information and outputs the generated data to thein-vehicle network 941.

6-3. Third Application Example

FIG. 17 is a block diagram showing an example of a schematicconfiguration of a wireless access point 950 to which the technology ofthe present disclosure can be applied. The wireless access point 950includes a controller 951, a memory 952, an input device 954, a displaydevice 955, a network interface 957, a wireless communication interface963, an antenna switch 964, and an antenna 965.

The controller 951 may be, for example, a CPU or a digital signalprocessor (DSP) and operates various functions (for example, accesslimitation, routing, encryption, a fire wall, and log management) of theInternet Protocol (IP) layer and higher layers of the wireless accesspoint 950. The memory 952 includes a RAM and a ROM and stores a programexecuted by the controller 951 and various kinds of control data (forexample, a terminal list, a routing table, an encryption key, securitysettings, and a log).

The input device 954 includes, for example, a button or a switch, andreceives a manipulation from a user. The display device 955 includes anLED lamp and displays an operation status of the wireless access point950.

The network interface 957 is a wired communication interface thatconnects the wireless access point 950 to a wired communication network958. The network interface 957 may include a plurality of connectionterminals. The wired communication network 958 may be a LAN such asEthernet (registered trademark) or may be a Wide Area Network (WAN).

The wireless communication interface 963 supports one or more wirelessLAN standards of IEEE 802.11a, 11g, 11n, 11ac, and 11ad, to supplywireless connection to a nearby terminal as an access point. Thewireless communication interface 963 can typically include a basebandprocessor, an RF circuit, and a power amplifier. The wirelesscommunication interface 963 may be a one-chip module in which a memorystoring a communication control program, a processor executing theprogram, and relevant circuits are integrated. The antenna switch 964switches a connection destination of the antenna 965 among a pluralityof circuits included in the wireless communication interface 963. Theantenna 965 includes one antenna element or a plurality of antennaelements and is used to transmit and receive a wireless signal throughthe wireless communication interface 963.

In the wireless access point 950 shown in FIG. 14, the data processingunit 11, the communication unit 12, and the control unit 17 describedwith reference to FIG. 2 may be mounted on the wireless communicationinterface 963. At least some of the functions may be mounted on thecontroller 951. For example, the control unit 17 determines a permittedtransmission time period on the basis of received requested transmissiontime periods, so that communication efficiency can be improved.

7. CONCLUSION

As described above, according to the first embodiment of the presentdisclosure, a frame is transmitted from a slave station in a permittedtransmission time period suitable for a situation of the slave station,and thus it is possible to reconcile efficient use of wirelesscommunication resources with stabilization of reception performance inwireless multiplex communication. Also, since a master station sidedetermines the permitted transmission time period and notifies the slavestation of the permitted transmission time period, a process ofdetermining a transmission time period is not performed on the slavestation side, and it is possible to achieve simplification of a processand power saving at the slave station. In addition, according to thesecond embodiment of the present disclosure, a slave station having nodata to be transmitted need only transmit an ACK frame, and atransmission time period is optimized, so that power consumption at theslave station can be reduced. In addition, according to the thirdembodiment of the present disclosure, in comparison with a case ofspace-division multiplexing trigger frames, a space-divisionmultiplexing process is omitted, and thus it is possible to simplify aprocess involved in transmission of trigger frames. In addition,according to the fourth embodiment of the present disclosure, even anapparatus and the like conforming to a wireless communication standardwhich does not support a space-division multiplexing scheme is includedamong application targets, and thus it is possible to further improvecommunication efficiency.

The preferred embodiment(s) of the present disclosure has/have beendescribed above with reference to the accompanying drawings, whilst thepresent disclosure is not limited to the above examples. A personskilled in the art may find various alterations and modifications withinthe scope of the appended claims, and it should be understood that theywill naturally come under the technical scope of the present disclosure.

For example, in the above embodiments, any one of communication stations10 is a master station or a slave station, but the present technology isnot limited to such examples. For example, an AP apparatus may operateas a master station, and a terminal apparatus may operate as a slavestation.

Also, a TRQ/TFB frame exchange process in the above embodiments may beperformed as a part of request to send (RTS)/clear to send (CTS) frameexchange.

Further, in the above embodiments, examples in which information such asrequested transmission time periods (RDR), a permitted transmission timeperiod (RDG), a flag (Split_Ack_Flag), and the like is stored in a MACheader or the like have been described, but the correspondinginformation may be stored at the end or an arbitrary position in a frameas shown in FIGS. 9, 13, 14, and the like.

Further, not only a process in which steps shown in the flowcharts ofthe above embodiments are performed in a time-series manner inaccordance with a described sequence but also a process in which thesteps are not necessarily processed in a time-series manner but areexecuted in parallel or individually is included. Also, it isself-evident that even steps processed in a time-series manner can beappropriately changed in sequence depending on circumstances.

Further, the effects described in this specification are merelyillustrative or exemplified effects, and are not limitative. That is,with or in the place of the above effects, the technology according tothe present disclosure may achieve other effects that are clear to thoseskilled in the art from the description of this specification.

Additionally, the present technology may also be configured as below.

(1)

A communication apparatus including:

a communication unit configured to receive frames including firstinformation from a plurality of other communication apparatuses andtransmit first frames including information indicating a firsttransmission time period to the plurality of other communicationapparatuses;

a control unit configured to determine the first transmission timeperiod on the basis of the plurality of pieces of first information; and

a processing unit configured to generate the first frames.

(2)

The communication apparatus according to (1),

wherein the first information includes information indicatingtransmission time periods desired to be used in transmission of userdata by the plurality of other communication apparatuses.

(3)

The communication apparatus according to (2),

wherein the control unit determines the first transmission time periodon the basis of a transmission time period longer than othertransmission time periods among the transmission time periods indicatedby respective pieces of the first information.

(4)

The communication apparatus according to (2) or (3),

wherein, when the first transmission time period determined on the basisof a transmission time period longer than other transmission timeperiods among the transmission time periods indicated by respectivepieces of the first information is greater than a threshold value, thecontrol unit determines the first transmission time period to be atransmission time period equal to or less than the threshold value.

(5)

The communication apparatus according to (4),

wherein the threshold value is determined on the basis of informationindicating a spare time of a wireless channel or information indicatingan amount of traffic relating to communication of the communicationapparatus.

(6)

The communication apparatus according to (4),

wherein the communication unit refrains from transmitting the firstframe to another communication apparatus which is a transmission sourceof a frame including first information indicating a transmission timeperiod greater than the threshold value.

(7)

The communication apparatus according to any one of (1) to (6),

wherein, when any one of the frames including the first informationindicates that one of the other communication apparatuses does notdesire to transmit user data as a response to the first frame, theprocessing unit includes information instructing transmission of anacknowledgement of the first frame in an independent transmission timeperiod in the first frame.

(8)

The communication apparatus according to any one of (1) to (7),

wherein the processing unit includes information designatingtransmission power used for frames transmitted from the plurality ofother communication apparatuses to the communication apparatus in thefirst frames.

(9)

The communication apparatus according to (8),

wherein the transmission power is designated so that a difference inreception power between the respective frames transmitted from theplurality of other communication apparatuses to the communicationapparatus is small at the communication apparatus.

(10)

The communication apparatus according to any one of (1) to (9),

wherein the frames including the first information include referencesignals, and

the communication unit transmits frames indicating a request fortransmission of frames including the first information to the pluralityof other communication apparatuses.

(11)

The communication apparatus according to (10),

wherein the frames including the first information are multiplexed byencoding the reference signals.

(12)

The communication apparatus according to (10) or (11),

wherein the processing unit acquires antenna weights on the basis of thereference signals, and

the communication unit space-division multiplexes the first frames usingthe antenna weights and transmits the multiplexed first frames to theplurality of other communication apparatuses.

(13)

The communication apparatus according to any one of (1) to (11),

wherein the communication unit frequency-division multiplexes the firstframes and transmits the multiplexed first frames to the plurality ofother communication apparatuses.

(14)

The communication apparatus according to any one of (1) to (11),

wherein the communication unit transmits the first frames to theplurality of other communication apparatuses using a multicastingscheme.

(15)

A communication apparatus including:

a communication unit configured to transmit a frame including firstinformation to a first communication apparatus, and receive a firstframe including information indicating a first transmission time perioddetermined by the first communication apparatus on the basis of aplurality of pieces of the first information; and

a processing unit configured to generate a frame on the basis of theinformation indicating the first transmission time period.

(16)

The communication apparatus according to (15),

wherein the processing unit generates the frame so that a transmissiontime period becomes the first transmission time period.

(17)

The communication apparatus according to (16),

wherein the processing unit generates the frame in which a frame that isan acknowledgement of the first frame is connected to user data.

(18)

The communication apparatus according to (16) or (17),

wherein, in generating the frame, the processing unit divides the framewhen the transmission time period of the frame exceeds the firsttransmission time period.

(19)

The communication apparatus according to any one of (16) to (18),

wherein, in generating the frame, the processing unit adds a padding tothe frame when the transmission time period of the frame is shorter thanthe first transmission time period.

(20)

A communication method including:

receiving frames including first information from a plurality of othercommunication apparatuses, and transmitting first frames includinginformation indicating a first transmission time period to the pluralityof other communication apparatuses;

determining the first transmission time period on the basis of theplurality of pieces of first information; and

generating the first frames.

(21)

A communication system including:

a communication unit configured to receive frames including firstinformation from a plurality of other communication apparatuses andtransmit first frames including information indicating a firsttransmission time period to the plurality of other communicationapparatuses;

a control unit configured to determine the first transmission timeperiod on the basis of the plurality of pieces of first information; and

a processing unit configured to generate the first frames.

(22)

A program causing a computer to implement:

a communication function of receiving frames including first informationfrom a plurality of other communication apparatuses, and transmittingfirst frames including information indicating a first transmission timeperiod to the plurality of other communication apparatuses;

a control function of determining the first transmission time period onthe basis of the plurality of pieces of first information; and

a processing function of generating the first frames.

REFERENCE SIGNS LIST

-   10 communication apparatus-   11 data processing unit-   12 communication unit-   13 modulation/demodulation unit-   14 signal processing unit-   15 channel estimation unit-   16 transceiver unit-   17 control unit

What claimed is:
 1. A first communication apparatus that operates as anon-Access Point (non-AP) station, and wirelessly communicates with anAccess Point (AP) communication apparatus based on IEEE802.11 standard,the first communication apparatus comprising: processing circuitryconfigured to: receive a request frame broadcasted by the APcommunication apparatus, wherein the request frame requests the firstcommunication apparatus and a second communication apparatus tosimultaneously transmit a first response frame and a second responseframe, the first response frame includes first feedback information toestimate a first weight of space-division multiplexing for the firstcommunication apparatus, and the second response frame includes secondfeedback information to estimate a second weight of space-divisionmultiplexing for the second communication apparatus; transmit the firstresponse frame to the AP communication apparatus in response to thereceived request frame, wherein the first response frame furtherincludes transmission data amount information of the first communicationapparatus; receive a trigger frame from the AP communication apparatus,wherein the trigger frame is generated based on the first response frameand the second response frame, the trigger frame is a trigger forsimultaneous transmission of a first data frame from the firstcommunication apparatus and a second data frame from the secondcommunication apparatus, and the trigger frame includes: identificationinformation that indicates the first communication apparatus and thesecond communication apparatus which are destinations of the triggerframe, transmission period information related to a common transmissiontime period for the first data frame and the second data frame,subcarrier information related to an allocated subcarrier for each ofthe first communication apparatus and the second communication apparatusto transmit the first data frame and the second data frame, and powerinformation related to a transmission power for each of the firstcommunication apparatus and the second communication apparatus totransmit the first data frame and the second data frame; and transmitthe first data frame to the AP communication apparatus in response tothe received trigger frame, based on the identification information, thetransmission period information, the subcarrier information, and thepower information, wherein the first data frame is transmittedsimultaneously with the second data frame, and a length of the firstdata frame and a length of the second data frame are determined based onthe common transmission time period.
 2. The first communicationapparatus according to claim 1, wherein the transmission periodinformation indicates a first transmission time period for the firstdata frame and the second data frame, and the processing circuitry isfurther configured to generate the first response frame so that a secondtransmission time period of the first response frame becomes the firsttransmission time period.
 3. The first communication apparatus accordingto claim 2, wherein the processing circuitry is further configured togenerate the first response frame in which a specific frame is connectedto user data, and the specific frame is an acknowledgement of thetrigger frame.
 4. The first communication apparatus according to claim2, wherein in the generation of the first response frame, the processingcircuitry is further configured to: determine the second transmissiontime period of the first response frame exceeds the first transmissiontime period; and divide the first response frame based on thedetermination.
 5. The first communication apparatus according to claim2, wherein in the generation of the first response frame, the processingcircuitry is further configured to pad the first response frame based onthe second transmission time period of the first response frame, and thesecond transmission time period of the first response frame is shorterthan the first transmission time period.
 6. The first communicationapparatus according to claim 2, wherein the processing circuitry isfurther configured to: calculate an amount of data to be transmittedbased on a transmission buffer of the first communication apparatus; andgenerate the first feedback information based on the calculated amountof data.
 7. A communication method, comprising: in a first communicationapparatus that operates as a non-Access Point (non-AP) station, andwirelessly communicates with an Access Point (AP) communicationapparatus based on IEEE802.11 standard: receiving a request framebroadcasted by the AP communication apparatus, wherein the request framerequests the first communication apparatus and a second communicationapparatus to simultaneously transmit a first response frame and a secondresponse frame, the first response frame includes first feedbackinformation to estimate a first weight of space-division multiplexingfor the first communication apparatus, and the second response frameincludes second feedback information to estimate a second weight ofspace-division multiplexing for the second communication apparatus;transmitting the first response frame to the AP communication apparatusin response to the received request frame, wherein the first responseframe further includes transmission data amount information of the firstcommunication apparatus; receiving a trigger frame from the APcommunication apparatus, wherein the trigger frame is generated based onthe first response frame and the second response frame, the triggerframe is a trigger for simultaneous transmission of a first data framefrom the first communication apparatus and a second data frame from thesecond communication apparatus, and the trigger frame includes:identification information that indicates the first communicationapparatus and the second communication apparatus which are destinationsof the trigger frame, transmission period information related to acommon transmission time period for the first data frame and the seconddata frame, subcarrier information related to an allocated subcarrierfor each of the first communication apparatus and the secondcommunication apparatus to transmit the first data frame and the seconddata frame, and power information related to a transmission power foreach of the first communication apparatus and the second communicationapparatus to transmit the first data frame and the second data frame;and transmitting the first data frame to the AP communication apparatusin response to the received trigger frame, based on the identificationinformation, the transmission period information, the subcarrierinformation, and the power information, wherein the first data frame istransmitted simultaneously with the second data frame, and a length ofthe first data frame and a length of the second data frame aredetermined based on the common transmission time period.
 8. Acommunication apparatus that operates as an Access Point (AP) station,and wirelessly communicates with a plurality of non-Access Point(non-AP) communication apparatuses based on IEEE802.11 standard, thecommunication apparatus comprising: processing circuitry configured to:transmit a request frame to the plurality of non-AP communicationapparatuses to request the plurality of non-AP communication apparatusesto simultaneously transmit a first response frame and a second responseframe, wherein the first response frame includes first feedbackinformation to estimate a first weight of space-division multiplexingfor a first non-AP communication apparatus of the plurality of non-APcommunication apparatuses, and the second response frame includes secondfeedback information to estimate a second weight of space-divisionmultiplexing for a second non-AP communication apparatus of theplurality of non-AP communication apparatuses; receive, in response tothe transmitted request frame, the first response frame from the firstnon-AP communication apparatus and the second response frame from thesecond non-AP communication apparatus, wherein the received firstresponse frame further includes transmission data amount information ofthe first non-AP communication apparatus; generate a trigger frame basedon the first response frame and the second response frame; transmit thetrigger frame to the first non-AP communication apparatus and the secondnon-AP communication apparatus, wherein the trigger frame is a triggerfor simultaneous transmission of a first data frame from the firstnon-AP communication apparatus and a second data frame from the secondnon-AP communication apparatus, and the trigger frame includes:identification information that indicates the first non-AP communicationapparatus and the second non-AP communication apparatus which aredestinations of the trigger frame, transmission period informationrelated to a common transmission time period for the first data frameand the second data frame, subcarrier information related to anallocated subcarrier for each of the first non-AP communicationapparatus and the second non-AP communication apparatus to transmit thefirst data frame and the second data frame, and power informationrelated to a transmission power for each of the first non-APcommunication apparatus and the second non-AP communication apparatus totransmit the first data frame and the second data frame; andsimultaneously receive the first data frame from the first non-APcommunication apparatus and the second data frame from the second non-APcommunication apparatus, wherein the first data frame is transmitted bythe first non-AP communication apparatus in response to the transmittedtrigger frame, based on the identification information, the transmissionperiod information, the subcarrier information, and the powerinformation, and a length of the first data frame and a length of thesecond data frame are determined based on the common transmission timeperiod.
 9. The communication apparatus according to claim 8, wherein theprocessing circuitry is further configured to: determine the firstresponse frame indicates that transmission of user data as a response tothe trigger frame is undesired by the first non-AP communicationapparatus; and insert, in the first response frame, specific informationinstructing transmission of an acknowledgement of the trigger frame inan independent transmission time period.
 10. The communication apparatusaccording to claim 8, wherein the processing circuitry is furtherconfigured to include the power information in the trigger frame. 11.The communication apparatus according to claim 8, wherein the processingcircuitry is further configured to designate the power information sothat a difference in reception power between the first response frameand the second response frame is smaller than a specific value.
 12. Thecommunication apparatus according to claim 8, wherein the first responseframe further includes reference signals, and the processing circuitryis further configured to transmit, to the plurality of non-APcommunication apparatuses, frames indicating a request for transmissionof the first response frame including the transmission data amountinformation.
 13. The communication apparatus according to claim 12,wherein the first response frame including the transmission data amountinformation is multiplexed by encoding the reference signals.
 14. Thecommunication apparatus according to claim 8, wherein the processingcircuitry is further configured to: frequency-division multiplex aplurality of trigger frames; and transmit the frequency-divisionmultiplexed plurality of trigger frames to the plurality of non-APcommunication apparatuses.
 15. The communication apparatus according toclaim 8, wherein the processing circuitry is further configured totransmit a plurality of trigger frames to the plurality of non-APcommunication apparatuses based on a multicasting scheme.
 16. Acommunication method, comprising: in a communication apparatus thatoperates as an Access Point (AP) station, and wirelessly communicateswith a plurality of non-Access Point (non-AP) communication apparatusesbased on IEEE802.11 standard: transmitting a request frame to theplurality of non-AP communication apparatuses to request the pluralityof non-AP communication apparatuses to simultaneously transmit a firstresponse frame and a second response frame, wherein the first responseframe includes first feedback information to estimate a first weight ofspace-division multiplexing for a first non-AP communication apparatusof the plurality of non-AP communication apparatuses, and the secondresponse frame includes second feedback information to estimate a secondweight of space-division multiplexing for a second non-AP communicationapparatus of the plurality of non-AP communication apparatuses;receiving, in response to the transmitted request frame, the firstresponse frame from the first non-AP communication apparatus and thesecond response frame from the second non-AP communication apparatus,wherein the received first response frame further includes transmissiondata amount information of the first non-AP communication apparatus;generating a trigger frame based on the first response frame and thesecond response frame; transmitting the trigger frame to the firstnon-AP communication apparatus and the second non-AP communicationapparatus, wherein the trigger frame is a trigger for simultaneoustransmission of a first data frame from the first non-AP communicationapparatus and a second data frame from the second non-AP communicationapparatus, and the trigger frame includes: identification informationthat indicates the first non-AP communication apparatus and the secondnon-AP communication apparatus which are destinations of the triggerframe, transmission period information related to a common transmissiontime period for the first data frame and the second data frame,subcarrier information related to an allocated subcarrier for each ofthe first non-AP communication apparatus and the second non-APcommunication apparatus to transmit the first data frame and the seconddata frame, and power information related to a transmission power foreach of the first non-AP communication apparatus and the second non-APcommunication apparatus to transmit the first data frame and the seconddata frame; and simultaneously receiving the first data frame from thefirst non-AP communication apparatus and the second data frame from thesecond non-AP communication apparatus, wherein the first data frame istransmitted by the first non-AP communication apparatus in response tothe transmitted trigger frame, based on the identification information,the transmission period information, the subcarrier information, and thepower information, and a length of the first data frame and a length ofthe second data frame are determined based on the common transmissiontime period.